I leave them in longer actually. For various reasons though. I'll start with Otos, the fry will snarf them better when they become more mushy. So until it floats to the top or becomes fuzzy, I leave them in there.
Now for my plecs...BNPs and Clowns. I just leave them in until gone which is usually about a day and a half. The BNPs in particular treat it like cotton candy when it gets to a certain point. I'll drop couple slices in, they'll pick at it. After about a day, then they act like ravenous pirhana's and just attack it like crazy. Fun to watch thats for sure. ;o)