We do tummy time a couple times a day. If he's really upset I set him on his tummy and settles down. He LOVES being on his tummy. (which is a nice treat, as DD HATED it) Actually most days he falls asleep during tummy time and ends up napping like that.
It's nice when they enjoy it. John tolerates it fairly well. A lot of times he will find his hands and suck on them and forget about picking his head up more lol. I am trying to do it 2-3 times a day for at least 5-10 minutes to get him working those muscles.
Tasha - how cool that Carter rolled!!