The baby fry will normally hatch anywhere from 1 to 2 days after betta fish spawning. Once hatched the tiny fry usually don't do very much at all except wiggle about. They usually after a small time they will wiggle their way out of the protective bubble nest. The male Betta fish has an extremely busy job ahead of him putting the fry back in the bubble nest and the ongoing maintainence of the nest. Simply put, it's a around the clock, 24-hour job for the male betta. If he misses any of the fallen fry, then there's a possibilty that they may not survive.
One thing is for sure you should not try and do the male betta fish job for him. Even if you do lose some of the newly born fry, trying to save them will more than likely disturb the rest of the tank as well as the nest itself. Also, this really does upset your male betta. It is much better to leave them alone at this point in time.
When Its Time To Remove The Male Betta
Usually about 2 days after the baby fry have hatched and figured out how to swim in the bolw. They generally leave the bubble nest and then tend to sit just under the water surface. The thing to watch here is that the male betta, has not eaten during the whole time and may start to eat a few of the fry. However, this does not mean this will happen, but you should keep a close eye on the breeding tank during this time. If this does start to occur however, then this is a signal to remove the male betta fish from the tank. He's done his job and really cannot help the baby fry any further.
It's best to transfer the male betta fish to a clean and warmer tank on his own. And it really is best to leave him on his own and not with other fish as he may get a bit aggressive during this time. You should then feed him some really high-quality fish food for about a week until he recovers from raising his baby fry.