Well, once you do the big water change and stop supplying ammonia, you will begin to lose bacteria but only at a tiny rate at first, pehaps 1% the first day, 2 the next, 4 the third, something like that. So if you can't manage it the very next day its not a disaster, although I think the common thing to to perhaps water change. In fact, the big water change is mostly to clear out nitrate(NO3), so you can actually dose ammonia -again- if you know you're going to have to go another day - it won't produce that much nitrate just once or twice. Just be sure all ammonia has cleared of course before releasing fish into the tank.
Its a weird feeling, switching to fish, because you no longer are dosing ammonia, but you keep up the testing in case you get a mini-cycle of any sort, in which case you switch to fish-in cycling behaviour immediately, of course.
It still takes a tank some more months to really settle in. I sometimes think that about 6 months is the sweet spot where one day you look at the tank and it just seems vibrant and perfect. After a good fishless cycle though, the fish (if you get a healthy batch) should look great from day one and stay that way.
WD