the rule is 4 weeks should be about right, however the last few times 4 weeks was a bit early for mine and 5 weeks was better. I just tell people after the 4 week period watch the male's mouth closely and if they are ready you should be able to see the fry moving in his mouth, then they are ready to collect.
As far as collecting I just take a net and catch the male, bring it close to surface and gently wiggle the net and the male should spit them out in the net for easy collecting. I usually get around 2 dozen each time.
as you stated put the fry in a breeder net/box in tank and feed them live baby brine shrimp and after a month or so wean them on frozen. Good Luck !