It does vary, and I would say between 4-5hrs is pretty standard. My LO is 13mos old and he does about 5.5-6hrs A time in the morning and 4.5-5hrs in the afternoon. This works out really well for him, but I know he is on the high side of A times. My DS1 couldn't handle A times that long at the same age and was still on two naps for quite awhile still.