There were only two bombs ready, and they were just barely beyond prototypes, if I recall correctly.

But they worked, were sufficiently weaponized, and we were already assembling the 3rd, although we were starting to hold back at that point, to give them time to decide to surrender, and giving us time to debate the proposition of using 5 or more in Operation Olympic, the invasion of southern Kyushuu scheduled in slightly less than 3 months.

(November 1st, although as it turns out a typhoon that hit Okinawa would have required delaying it, which in turn would have totally screwed the timetable of Operation Coronet, the invasion of the Honshuu Kantou plain where Tokyo etc. were, due to weather.)