Knock wood, I've never had trouble w that - depending on how big the cast and theater (and how much I am trying to catch up on during the break) either I or my assistant walk around to announce that we are at 1 or 2 minutes and then (1 or 2 minutes later) that we're back. As in "and we're back". This gives folks that moment to close things up and/or hit the loo, and for me to gather the director or choreo or whomever and get them back inside the theater, and then everyone is back, quiet and ready in time to start. Maybe it's just luck, but I've done this for years now and, well, so far, it has worked nicely.