I leave them for 2.5 hours. I had at least one who screamed the whole time for the first few weeks, but these children had only ever been rocked and/or nursed to sleep. Now, they all sleep very well, and sometimes I have to wake them up when they sleep past the 2.5 hour mark (parents do not want them to sleep more than that). It was the wise advice from women on this board that made me try the cry-it-out method and I'm sold. All the parents think I'm some kind of miracle worker because their children nap at my house and are cheerful in the evening. None of these children will nap at home, which I don't understand, except that I suspect the child knows if they cry the parent will rescue them LOL