There is no cut off date it depends on the context and who recognises. These examples are all very different. Time is a factor but not the only thing; International support/opinion is more important.

- Kaliningrad - Ultimately the legitimacy for this annexation comes from the Allies support for Soviet sovereignty out of the Potsdam Conference. The US and UK supported it, which means all the occupying powers of Europe supported it.

- Tibet - China, both the ROC and PRC have always claimed Tibet as part of the historical territory of China. Tibet was never recognised by any country (*major powers, except India for a short while) as a sovereign independent nation. There have been treaties that discussed its internal autonomy and independent administration, but these treaties also made clear that China was either the suzereign or the sovereign. Whilst the predominant western perspective towards China's actions during this time is one of conquest and expansion, the Chinese perspective would be one of a reclamation of former borders and territory that existed within their lifetimes (not mythical), unifying an integral nation fractured by crisis (Sino-Japan War, Civil War etc).

- Goa - The annexation of Goa was thoroughly condemned by the western world and there is even some recognition within India that the annexation was "illegal". However, the focus of condemnation was on the use of force, most nations held the view that Goa was "Indian". They did try to negotiate, but the Portuguese position was; that Goa was not a colony but part of metropolitan Portugal, its transfer was non-negotiable and India did not have legal standing to make claim to it. Obviously, at the time neither the Indian government or people probably had no time for such arguments. Whilst it probably was "illegal" they had enough international support (especially from former colonised states and the Soviet Union) and Goa was too small and insignificant a territory for anyone to put up too much of a fuss. When the Authoritarian regime in Portugal fell in 1974 the new government recognised Indian sovereignty over Goa.

- Northern Cyprus - As you mention is only recognised by Turkey. Unless someone goes there to physically remove them (and consequently defend from Turkey), then the only option you have is to refuse recognition. Now given Turkey is a NATO member, solid military power and strategic ally of the US, it's probably the case that most other nations "tolerate" their occupation but refuse to legitimise it. Turkey have also in this case used an old imperial trick, Northern Cyprus is not territory of Turkey proper its set up as an independent state.

- Golan Heights - It's odd. Technically speaking Israel has not formally annexed the Golan Heights, it has just extended Israeli "law, jurisdiction and administration". This is seen as a de facto annexation, yet at the same time the Golan Heights are frequently used as a bargaining chip or an offer to get Syria round the negotiating table. I think the case here is that whilst Israel are perfectly prepared to annex it and probably would like to, its ultimately not integral territory to them and much harder to give away once its formally taken. Now if you are another country looking into this situation why recognise something you may have roll back on in future, that could damage your relations with other Arab/Muslim states, and is on shaky legal footing. Even though Israel's claim is it's won in a "defensive war", I dont think the international community wants to set up such a precedent. The line between defensive/offensive can be really blurry when considering inter-generational conflict, preemptive strikes, covert operations etc.

Israel has nukes too

Yes but it's also very vulnerable to nukes as well. Just 1 or 2 would do the job. Russia, China, India can take a beating and maybe still have something left to give. Its less to do with nukes and more to do with having huge populations, deep territory, indigenous production, military and diplomatic clout etc. It's not about having nukes, it's about the reality of diplomatic/military conflict with (potential) great powers vs regional.

Australia

As an Australian citizen, while our nation exists on Indigenous land, our nation's existence is recognised worldwide despite our lack of nukes. Does our record of injustice against Indigenous people jeopardise our continued international recognition?

Essentially no. If the indigenous people could organise, gain international support and provide real deterrence or opposition (i.e violence, major social/political movement), they could shape the situation to a point where this could become a possibility. But the nature of settler-colonialism is such that you are trying to prevent that from day one by disrupting indigenous ways of life, divide and rule, repression, international isolation etc. Once that process has taken place to the extent it has in Australia, Canada, the United States etc, what real possibility do the indigenous have to challenge it. Historically speaking Australia probably benefits from the fact it was formed at a time where the international norms of today, self determination, opposition to imperialism, plurality, racial equality did not really exist. Some countries are also in this situation and have either been grandfathered in or are in a position where no alternative power can really displace them.

EDIT: I know in some parts re: why don't people recognise Golan/N.Cyprus there is some speculation on what other nations actual positions and reasonings for recognising or not are but I would like to say that these decisions are opaque, political and multidimensional, which makes it difficult to summarise their actual positions without going into huge amounts of detail on international relationships at various points in time. I've tried my best to summarise the overall vibe and most likely position of most nations.

EDIT 2: In relation to cut-off time specifically, it's not the case that there were any legal prescriptions regarding this time, but more the case that after WW2 and the end of imperialism there were many "unresolved" issues around the world. Many of these examples have history that predates the world wars or are in some cases historic relationships that needed to be formalised into the international system (borders, nation-states, who is sovereign etc).

[Part 1/2]

Some factual background and important clarifications on the Golan Heights to begin with:

In June 1967, Israel began occupying the Golan Heights. The Knesset on 14 December 1981 passed the Golan Heights Law (Golan Heights Law, 1981, 36 LSI 7) that brought the Golan Heights under the “law, jurisdiction and administration” of Israel, which is broadly agreed to constitute annexation, or at least a very strong step towards annexation (see e.g. Asher Maoz, “Application of Israeli Law to the Golan Heights is Annexation” (1994) 20 Brooklyn Journal of International Law 355; Adam Roberts, "Prolonged Military Occupation: The Israeli-Occupied Territories since 1967” (1990) 84 AJIL 44, 60).

For completeness, it is important to note that there are some academics who argue that the Golan Heights Law does not constitute annexation, and that Israel is merely occupying the Golan Heights as a belligerent occupying power (legal under international law) rather than annexing it to its sovereign territory (illegal under international law): see e.g. Zemach, "Can Occupation Resulting from a War of Self-Defense become Illegal?" (2015) Minnesota Journal of International Law, 316, 334; Sheleff, “Application of Israeli Law to the Golan Heights is Not Annexation” (1994) 20 Brooklyn Journal of International Law 333.

However, that Israel did annex the Golan Heights seems to be the majority position, because 3 days later on 17 December 1981, the UNSC saw the need to adopt Resolution 497 that declared the law “null and void and without international legal effect” and demanded that Israel rescind the law. Of note is that all 15 member States of the UNSC voted for the Resolution unanimously, including the USA. However, a proposed stronger resolution that “all member states should consider applying concrete and effective measures in order to nullify the Israeli annexation of the Syrian Golan Heights” was vetoed by the USA (“United States Recognizes Israeli Sovereignty Over the Golan Heights” (2019) 113 AJIL 613, 616).

In 2019, as OP pointed out, the USA changed course and recognised Israeli sovereignty over the Golan Heights, with Secretary of State Pompeo interpreting SC Resolution 497 as “provid[ing] that Israel would withdraw from some—but not necessarily all—territory captured in 1967” (ibid, 617). [You can read Resolution 497 for yourself and decide if you agree.] When questioned by Senator Durbin of Illinois on how the USA could condemn the annexation of Crimea by Russia on the one hand while recognising the Israeli annexation of the Golan Heights on the other, Secretary Pompeo stated that:

The Israelis ended up with the Golan Heights as the result of having been attacked… and they defended themselves, and they retained that terrain to continue to defend themselves from the murderous regimes in Syria. Russia, on the other hand, wasn’t on the defensive. Russia chose at their own moment in time to go seize land from a people that posed no threat to them whatsoever. (ibid, 617)

This seemed to have been the legal position of the Trump Administration, which is at odds with the general international law position that does not distinguish between offensive and defensive wars when considering the illegality of annexation. Yoram Dinstein summarises the general position of the international community in respect of the Golan Heights (The International Law of Belligerent Occupation, CUP 2009, 19):

After more than forty years, there is no treaty of peace between Israel and Syria: several rounds of hostilities have merely been punctuated by ceasefires. As long as the state of war between the two countries is not terminated, the Golan Heights are under Israeli belligerent occupation.

Under international law, belligerent occupation does not confer sovereignty: per Professor Oppenheim (considered one of the giants of public international law), an occupying power does not have even an “atom of sovereignty”. (Oppenheim, “The Legal Relations between an Occupying Power and the Inhabitants” (1917) 33 LQR 363, 364) This proposition is codified in art 47 of Geneva Convention IV and art 4 of Protocol I to the Conventions, and is now generally accepted as insuperable. (Benvenisti, The International Law of Occupation (Princeton University Press 2004, 5-6; Dinstein, op. cit. 50).

In light of this, the editors of the American Journal of International Law wryly note that “the [US] State Department did not provide a public explanation regarding how the U.S. recognition of the Golan Heights as part of Israel was consistent with international law”. (op. cit., 617)

So the broad position seems to be that international law does not recognise Israeli sovereignty over Goa, with Israel and the USA being the exceptions.

But that doesn’t answer OP’s wider question. I’m afraid it admits of no easy answer. The short answer is “we don’t know”. International law is fluid and constantly evolving, there is often no consensus, and answers to hard questions often depends on who you ask. I’ll use the example of India’s annexation of Goa to illustrate this. [See child comment below]