Manage dynamic schedules

I manage a small machine shop in California with about 20 CNC machines (all our work is job shop type work). I recently had a VP wander through my shop, and he noticed that six of the machines were on setup. He has previously stated that he ran a machine shop in the past and I frequently get inquiries from him. This time however he stated that he does not understand how 6 machine can be on setup simultaneously. He has further asked if I can develop a process to minimize the number of machines on setup simultaneously. Does anyone have a good method for doing this?