One word of warning about Platonic dialogues in general, and those two in particular. The dialogues are an odd genre, where speculation and on the spot myth-making are used to demonstrate philosophical points and where any character can say anything as long as the other characters don't object to it. There are a lot of times in these where one character says something very like 'now this is crazy, but just for the sake of argument, hear me out' or antoher says, roughly 'that's nuts, but I'm going to roll with it.' The purpose of the dialogues is to explore the true nature of human society, the soul, knowledge, existence etc. through a conversation, not to illustrate historical fact, or even to demonstrate agreed-upon or commonly held beliefs - 'the myths' of Plato, including the famous allegory of the the cave, are often illustrations of philosophy rather than anthropological records of common beliefs in 4th century Athens. So the dialogues in general must be read with care - don't assume anything in them is meant to be taken at face value. Timeus starts out as a sequel to the 'City in Speech' from the Republic, where one interlocutor wants to see the 'City in Speech' engaged in war. So the dialogue describes a war between Atlantis and an ancient Athens, which continues in Critias. The important thing to remember is that the entire story is being used to illustrate how the ideal, hypothetical state from the Republic would work 'in action.' Since the story is being used to illustrate a purely hypothetical situation for the sake of philosophical argument, we should be cautious about assuming that anything in the dialogue is even intended as history, including extraordinary archives.

Besides what /u/WARitter (correctly) says, the reference in the Timaeus to the temple of Neith (I can't remember any reference in the Critias, all that's mentioned are Egyptian priests) is simply impossible, apart from the really pretty transparent allegorical nature of the entire dialogue. In the Timaeus it's said that Critias is getting the story he's telling from his grandfather, who got it from Solon, who in turn got it from the priests of Athena at Sais, whom the Egyptians call Neith, but which Solon lamentably never wrote down. Now that's a classically Platonic conceit--Plato very frequently has his characters claim that they got their fanciful stories (or sometimes not so fanciful--the entire Symposium is related indirectly like this) from a guy who knew a guy who heard it from another guy who once saw this dude in the street. Part of Plato's reason for always doing this is to distance himself and the reader from the allegory that's being related, and make it even clearer that, as /u/WARitter has pointed out, this is all just philosophical deliberation. Nor is there any reason to suppose that Solon ever went to Egypt and talked with Egyptian priests--besides, Critias specifically says that Solon never wrote this down, it's pure hearsay. More importantly, however, if we want to try to brush aside problems of Platonic convention and allegory and really want to imagine that Plato is somehow really referring to some story that he actually heard, we're faced with the fact that what Critias claims that his grandfather told him that Solon told him that he heard from a priest is simply not possible, nor is what Wikipedia says really what it says in Plato. In the Timaeus Critias claims that this is what the priest told Solon, regarding the texts at Sais:

προτέραν μὲν τὴν παρ ὑμῖν ἔτεσιν χιλίοις, ἐκ Γῆς τε καὶ Ἡφαίστου τὸ σπέρμα παραλαβοῦσα ὑμῶν, τήνδε δὲ ὑστέραν. τῆς δὲ ἐνθάδε διακοσμήσεως παρ᾽ ἡμῖν ἐν τοῖς ἱεροῖς γράμμασιν ὀκτακισχιλίων ἐτῶν ἀριθμὸς γέγραπται. περὶ δὴ τῶν ἐνακισχίλια γεγονότων ἔτη πολιτῶν σοι δηλώσω διὰ βραχέων νόμους, καὶ τῶν ἔργων αὐτοῖς ὃ κάλλιστον ἐπράχθη: τὸ δ᾽ ἀκριβὲς περὶ πάντων ἐφεξῆς εἰς αὖθις κατὰ σχολὴν αὐτὰ τὰ γράμματα λαβόντες διέξιμεν.

For she [Athena] founded your city a thousand years earlier, having received the seed from Gaia and Hephaestus, then [a thousand years] later she founded ours. The age of the constitution [διακόσμησις, really a "regulation," but Plato means the body of laws constituted at the foundation of the city] here is written as eight thousand years in our sacred texts. But regarding your citizens nine thousand years ago I will briefly show you through their laws and of their work which was done most splendidly: the exact nature of everything we will go and peruse afterward, at leisure, in the sacred texts themselves.

Note that what Wikipedia claims Plato says is not what Plato says. Plato says that Critias said that his grandfather told him that Solon told him that he heard from a priest that there were sacred (not "secret," Wikipedia made that up--hell, the priest says that Solon can check them out for himself whenever he feels like it) texts at Sais that said that the age of the foundation of the city of Sais was eight thousand years earlier. Plato most certainly does not say that the texts themselves were eight thousand or nine thousand years old (Wikipedia seems to be confusing, deliberately or not, the dates that Solon's priestly interlocutor gives for Athens and Sais), and of course if Plato did in fact say what Wikipedia wants him to say (which we've seen he doesn't) it would be simply impossible--Egyptian writing was not developed for something like six thousand years after Plato's supposed foundation-date of Sais, so how on earth could we find anything written from that early?

Everything that the priest says here is certainly made up, a fact which was recognized in antiquity--the suggestion that Atlantis was a real place and that Plato's story describes some sort of actual earlier civilization first appears in the late 19th Century. Egypt was well-established in Platonic thought as being a sort of mystical source of ancient knowledge, and Egyptian sacred texts are the Platonic equivalent of seekreet dokuments that allow the reader to suspend his disbelief. Likewise, Solon (who, as Critias laments, never wrote the story down) was, as is pointed out in the Timaeus the wisest of the seven sages and therefore holds an equivalent position to the transmission of the allegory.

Can I get a link to the page you got this from?