We don't know whether atomic bombs would have been used on, say, Berlin or the Ruhr area (maybe even tactically, to speed up the allied advance in the west), but I think the USA would have used one, if only to send a message to the soviets.
There is also strong evidence that Stalin wanted to get to berlin first to grab some of the German nuclear materiel in Berlin
The timelines, the actual dates that the bombs became available, are a little secondary imho as this was a multi-year developmental program. I still doubt they would have dropped a bomb on germany for a variety of reasons both technological and sociological.
US bombing in Germany was designed to specifically attack industry. They flew during daytime, despite that leading to much higher causalities among their crews, and used bomb targets.
It was the UK that firebombed Dresden during night without bothering to aim at specific targets. The British always flew night raids and just aimed to cause carnage.
American policy on the Western campaign didn't target civilians. They used precision bombing (what it was called at the time, it wasn't very precise) to target real targets.
Yet, the policy against Japan ended up much different. At the beginning precision bombing was attempted. But by 1945 they started to resort to firebombing entire cities.
I wonder if there was a racial aspect to it. A lot of Americans consider themselves ethnically German.
The USAAF conducted firebombing of German cities, notably Hamburg.
Another aspect not covered in the OP is the efficiency of US nukes. Much/most of the damage done was not from the bombs. If you measure damage through the heat energy released, most came from the burning of the cities rather from the fission in the bomb itself. The firebombing of a city releases as much energy as a nuclear explosion, doing a comparable amount of damage. At the time, a firebombing raid required fewer resources than a nuke. So, from an energy standpoint, the nukes were not an economical means of destroying Japanese cities.
Why then were they used? Why were they used in the pacific and not in europe? (Insert massive screaming rants here.)