Paula,
I'm not sure from your description whether the time you are concerned about is while the teams are working to decide on and answer or whether its answering questions after the simultaneous reports. I don't get many complaints about either. I think the thing that helps me most with the pre-report time is that I give students a time they need to finish that I think will push them pretty hard and project it with a PowerPoint count-down timer. Then I circulate among the teams to keep tabs on how close they are to close to finishing in the time they were given. If it looks like MOST teams are not going to make it, I'll add a few minutes for everyone. Otherwise when the timer hits zero, I call time and move ahead. As for managing the time after the teams do their simultaneous report, I simply make sure that I keep the discussion on track and moving along.
Larry