I get the children into bed at approximately the same time every day but sometimes we are 15 minutes to a half hour off when we are outside too long. Then the children sleep for 2 to 2 1/2 hours and I don't wake them. I let them wake as naturally as possible. However, if they are still asleep over 3 hours I start opening the curtains slowly so we can stay on schedule for afternoon snacktime. So I'm not anal about watching the clock but they all must stay as quiet as possible for at least 2 1/2 hours to allow for the child who needs that much sleep unless they all wake up earlier.