Three days doesn't seem like a reasonable amount of time for Japan to survey the damage of Hiroshima and discuss surrender; it took them a further six days after Nagasaki was bombed.
I've looked into this myself a bit and found a lot of conflicting information. Some things I read say that Japan was ready to surrender before Hiroshima, others say that they doubted the US had more than 2 or 3 additional bombs readied (they actually only had the one) and were willing to weather more attacks. Unless I'm mistaken, they made no official announcement of their intentions one way or the other.
Even if Hiroshima wasn't enough motivation, perhaps USSR declaring war (and invading on three fronts) would have tipped the scales. This happened only a day before Nagasaki was bombed.
Wouldn't it have been worth it to wait a few extra days, or maybe even a couple of weeks, before killing 39,000-80,000 civilians?
/u/restricteddata gave an excellent reply to a similar question, a few weeks ago:
It's not an easy question to answer and historians have argued about it for awhile[1] . To put it simply, it is fairly easy to explain the bombing of Hiroshima in terms of strategy and planning. It is well-documented. There are a lot of different motivations, including thoughts about the postwar situation (which includes the Soviets). The second bomb (intended for Kokura[2] but dropped on Nagasaki instead) is more troublesome. In hindsight, the official narrative was always about how, well, one bomb didn't do it, maybe a second was needed. But there is no real evidence from the time that anybody thought that way. And it misunderstands the role of "strategy" in the actual dropping of the bombs — the question of a second bomb was never deliberated at the high levels. The way it worked is something like this. The idea was to have several bombs to use, eventually, but most strategic discussion focused on the first bomb. The official bombing authorization[3] of late July 1945, however, said that: Additional bombs will be delivered on the above targets as soon as made ready by the project staff. Further instructions will be issued concerning targets other than those listed above. So it was an extremely open-ended order. The initial bombing date was "after about 3 August 1945," and the first date that gave good weather for the bombing was August 6th. That became the Hiroshima bombing. The next one was scheduled for sometime around August 11th, but the weather forecast looked poor, so it was dropped on August 9th instead. Which is to say, the close proximity of the two bombs — within 3 days of each other, as opposed to 5 days of each other — was not due to high strategy, but to weather forecasts, and was decided by the people on the ground on the island of Tinian, not politicians in Washington. This is of relevance to the question because there are a lot of people who think the bombing of Hiroshima is justified, but when you get into the question of Nagasaki it gets more murky. Three days is not adequate time for a government to make a major decision; it is not really even adequate time for a government to assess what has happened (whether it was really an atomic bomb, what the damages were like, etc.). I think it is telling that immediately after Nagasaki, Truman issues an order that said, in essence, no more atomic bombing until I authorize it explicitly.[4] (And there were additional bombs being readied.) I see this as a re-assertion of control from someone who realizes that major geopolitical decisions are being made by local airmen. There are different interpretations for why two bombs were slated to be used at all[5] . Personally I lean towards the one that it wasn't actually part of some grand design. They had two bombs ready to go and they had a blanket order to bomb as they saw fit and they used them as such. I don't think it was due to high strategy whatsoever — the people who made the decisions on the ground were not concerned with Russia or anything else; they didn't even particularly regard the bomb as being something unusual, just another weapon.
"The original schedule devised on Tinian slated Fat Man for use over Japan on August 11, but a forecast of deteriorating weather starting on the tenth and extending for five days ignited a rush to execute the mission on August 9."
Source: Downfall: the End of the Imperial Japanese Empire by Richard Frank,
Downfall is a vital book for readers interested in the last months of the Pacific War, whether Hiroshima/Nagasaki was justified, the US plans for Olympic and Coronet, etc.
Everything I've read about the Bombings indicated that the Interim Committee wanted to provide the illusion of a production line of atomic bombs, when in fact, Tibbets' unit dropped the only two the U.S. Had in stock until early September.
One was being shipped to Wendover for Transit to Tinian, but whether or not its Plutonium Core was ready was made unclear (this is from a conversation that Paul Tibbets had with Studs Terkel).