I don't think everyone who clicked the stone got a question answered, but people generally don't. I dunno if anyone has ever sat down and timed out and charted all the M&Gs but they rarely go over an hour. These vary, though. The last one I think I attended there were only three people there and I asked a series of questions because we had so much extra time.
I will say it's a little frustrating when someone clicks the stone, gets called up, and then doesn't actually ask a question. They are AFK or they waste time by saying something like 'oh I didn't really have a question, just wanted to say hi/give me your clothes.'