I've only done open (and a bit of accidental!) pollination where the males and females grow together in the same tent until I don't need the male plants anymore. (Project Psychonaut and Project Sam if you're interested.) Then I save the male flowers for their pollen to use for crosses later. Ideally, if you want lots of seed, apply pollen as soon as you have lots of pretty while stigmas at all the bud sites. You'll get a much bigger percentage of mature seeds for your efforts. Just be sure to let the buds mature before chop like you would with sinsemilla. I goofed a bit with Project Psychonaut and chopped when the sativa-dominant buds were dropping seed all over the floor. The more indica-dominant ones weren't as ready and too many ended up fit only for birds or hippies to eat.
One of my current grows, Project Murcott is partly for an F1 cross of Kosher Kush x Crockett's Tangie aka 24kt Gold. I'm doing it that way because I couldn't get KK regular seed but I could get feminized. I decided I absolutely did not need to wait to make that cross in a later grow since I only needed to pop one KK seed to get a female.