I wanted to wish you a good luck as well.
Our coaches have always had a set "warm-up routine" that the girls know for the open warm-up period. They establish the routine prior to the meet. It goes something like run a couple laps, skip a couple laps, high knees, etc. until their blood flowing. This is followed by some ground stretches like splits, pike, bridges, etc. This is either done in a line or a circle, depending on team size, room on floor and preference. Next, is straight line tumbling. Most teams start to form lines at about the same time and run through their beam and floor tumbling/dance. That usually takes up the open warm up period. Do you have a couple older girls that can possibly lead the team in stretching (they will need to remember what to do)? There are a couple teams in our area that will also use this time to jump on bars for a warm-up.
After general warm-up and march in, you will get warm-up time on each event. You should know the amount of time allotted to your gymnasts, it's probably determined by Xcel level and will be in the rules somewhere. Beam always seems to go the quickest and bars always seems to take the longest (just my observations as a parent).
Let us know how it goes!