I think it takes about a month I think, can't say for sure I have myself a berried F been berried for about 3 weeks and the eggs are starting to lighten up quite a bit I think it will be any day now. Good luck with them!!
3-4 weeks sounds about right... The moms, other shrimp, and fish will eat them, so I'd suggest a nursery/hatchery tank if you want to give them a chance to grow up.
