Prop, I think you're on to something. When I hold seminars, I never give a five or ten minute break. I always say "Let's take a (7 or 13 or 11) minute break. Let's start again X minutes from now and tap my wrist (although I don't wear a watch).
If you say "take five" people usually come back when they *feel* like five minutes have passed. But with the explicit instructions, most will look at their watch (or cell phone), do the math, and usually start right when we need to.
