Basically, how can you make sure that the atomic bomb is not developed before the start of X-Day (November 1, 1945) and Y-Day (March 1, 1946)? X-Day is the invasion of Kyushu and Y-Day is the invasion of Honshu. I shouldn't think it would be too hard to delay the production, and I don't think it would much affect the war in Europe. Or maybe the bombs have to be used on Germany and are unavailable before the invasion, but something tells me if we're still fighting Germany at that point there's less of a chance that X-Day goes off on time. So yeah, how can we make it so the atomic bomb is not yet developed when the invasion of Japan rolls around?