oh dear, you have quite a lot of research to do. I suggest first checking out the pinned topics in this forum, and then i suggest seperating your male and female. it's generally very bad practice to keep them together, as well as to breed lfs stock.
but since it's been done, remove the female so the male doesn't kill her. I don't know how long the eggs take exactly, i think maybe 48-72 hours/ someone who's bred bttas before will tell you better, but you won't be able to feed the babies flake, they need live food (baby brine shrimp). They also need to be in a heated tank and you will need enough room for them to growout to the boisterous juvies they ar going to be, and then you will have to seperate out all the males, and maybe some females. Bettas are not platies. They all pretty much hate one another.
To be honest, if this is a community tank you will be very lucky to have any fry survive. You will be lucky to have any survive regardless as baby bettas are very delicate.
[edit] forgive me if this sounds preachy at all, or you already know all that. we have a lot of folk come in who don't realize how much work is involved with bettas. as babies they are virtually incapable of dealing with anything but prime conditions and asking how long the eggs take to hatch sounds to me like you did not research it first.