It's all about being prepared ahead of time. We've been running a competition at the school I coach at for 10 years now, I took over 2 years ago.
Definitely have 2 panels of judges. This is KEY in making sure that everything stays on time. I also put a parent at the judges table to collect scores and keep them moving. Once the judges are ready for the next team she gives the thumbs up to the DJ/MC to announce the next team and to the parent that lets each team on the floor. These 3 people working together are the bread and butter for keeping a competition on time. There is NO reason a competition can't run on time and it makes me NUTTY when I go to comps that don't run on time.
We use our competition as a fundraiser for our girls, so the parents are required to work all day. Dads usually do the security and man the doors. At the beginning of the season I ask for volunteers to be chairs of each small committee and then they report to me with updates. I divide it into
Food (see if places will donate things or give you discounted prices..Chick Fil A)
Vendors
Admission
Spirit table (shout outs, flowers, beads, raffle baskets)
score room
programs, sponsors (if you're going to do them)
As a coach I take care of team registrations coming in, making the order of competition, ordering trophies, and answering emails from coaches and sending emails to them the week of the competition with the schedule, and important info.
Hope this helps :)