In OTL Japan surrendered just after the 2nd Atom bomb and the USSR declared war. (Ed Murrow suggested at the time that it was not clear which event caused the surrender.
However
1) WI the bombs were available a month earlier.
2) WI Japan had not surrendered despite both the bombs and the Soviet Union.
3) WI Japan had surrendered conditionally some time before August.
4) WI the bomb had not been available until say September.
1. The war would have ended a month earlier.
2. Truman and the entire War and Navy Departments were very reluctant to invade, given the experience of the meat grinder on Okinawa. Don't get me wrong, they would have done it if it was necessary, but no one looked forward to it. Given the presence of the bombs, we would have continued to nuke the home islands until they did surrender, or until there was nothing left. The Soviets would have taken at least part of Hokkaido.
3. I heartily agree with the above post. It was far, far too late for a conditional surrender. FDR would have never accepted it.
4. Conventional air raids and the naval blockade would have continued until the bombs were available, then they would have been used. There is a small possibility that the Japanese government would have collapsed given an extra month, however, the political situation in Japan was very dynamic at the time and it is virtually impossible to accurately speculate on what might have happened. It is my personal opinion that without the shock value of the bombs the Japanese would have fought on until there was nothing left.
Dave
www.pigboats.com