It takes patience. It is somewhere around 25-30 days. You can see the eggs in the shrimp. They are always cleaning them. This is a somewhat educated guess, just from experiance. My first sighting was purely coincidental with watching the tank late evening and luckily observing the happening. Lights switched off and I immediately turned them on for 15 added minutes. Live food gives your fish nutrients that nothing but live food can give them. I think if you can't have shrimp, purchased brine at least once a week is essential. Wash them first in fine stainless steel seive, or plastic. then feed. You have lots of live rock, over time, 6 months and beyond, lots of live stuff from rocks are also beneficial. Takes several months to establish. There are some crabs and such that feast on shrimp so check what you have that might totally nullify your shrimp purchase. Some fish also eat shrimp. My harliquins used to eat them. Banded goby used to pick them up and throw them against a rock. Was amazed to see that. He also did the same with hermit crabs. The only aggressive fish I can't catch is the six line wrasse. Am so sorry for putting thiat freeby fish in. Huge mistake.