How to leave or silence a group ichat? I keep company with night owls. Also, I have an iPhone 4s. Oftentimes, my friends include me in group ichats that start at a reasonable hour, but continue into the middle of the night. Every time I get a group ichat, or any text, my phone vibrates. I want to keep it this way -- except for late night group chats.

Is there any way to mute or leave group ichats?
Do not disturb is a feature that isn't supported in iOS 5.