A.K.
I think "quiet time" is great for both parents and kids, but it is not a form of discipline or punishment. My son (who is now 5) has had quiet time each day since the time he stopped napping. It is just a time when he has to play quietly in his room, and since it coincides with my daughter's nap time, it gives me some much needed "alone time" to get things done or just rest. He has a timer with a night-light on it that comes on to signal the end of his quiet time. When the light comes on he has to clean up his room, and then he can come out. When we first started it was only 30 min, but now is about 2 hrs each afternoon (and sometimes he stays longer because he gets caught up in whatever he is doing and does not notice his light). As I said before this is not a punishment, it is just something that happens each day, like nap time for younger children. We actually tried to make it a "special" time by getting him books on CD to listen to. We would go to the library each week and pick out the stories he wanted to listen to that week. We never locked the door to his room, but did have a baby gate when he was younger. That way he stayed in, but we could still easily keep tabs on what he was doing.
As far as the comments he is making, I would not bother to respond. Just ignore it. If you you start responding to it you are giving him exactly what he wants, attention.