I don't have specific times of the day that I put Micah down for his nap, but he is pretty consistent with being tried after being up for about 2 hours. My question is when you say you let him sleep when he's tired and be awake when he's not, do you mean he doesn't nap at the same time every day or he sleeps literally whenever he falls asleep (i.e. he's playing in his jumper and falls asleep so he must be tired...put him in bed)?
My LO is so alert that he pretty much forces him to stay awake. When he's tired we have to "help" him fall asleep (i.e. bring him to his room/feed him/rock him, whatever). He has never been one to just fall asleep in our arms while we're holding him or anything like that so I'm just curious about other babies.