How long until a Mickey Mousse Platy pops?

[35galSaltwater]

I am used to saltwater and havent done any breeding but I have the school's fresh water tank at my house for the extended winter break. Anyway, a little platy girl looks like she swallowed a ball, sits in a hang-on breeder box now... how long from looking reaaally pregnant until I see the fry? Anything else I need to know other than expecting life birth, mom needs extra feedings?
Thanks!