if you put it in at night and it is still there in the morning take it out. Some people say 5 mins, but usually I get up in the middle of the night to pee and if there is uneaten food in my tanks I take it out then, but if you want to sit around and watch them in the dark that is pretty cool too. Will give you some insight on their hunting and nightime activity. You'll be suprised how alive your tank is when it's dark. If you watch in the dark for 30-an hour and they don't eat it, you are probably safe to take it out, but if you don't have time to sit around and you have a strong filtration system you can leave it in there til the morning and remove uneaten/fish vomit in the morning. Has your fish began to eat yet? Hope you have that larger tank on the way.