It doesn't matter a single bit except MAYBE to your admin.

You get 28 minutes, during the last 2 of which the teams may take the field to stretch and warm up. If the other side takes 20, you have 26 minutes for your side.

Is it fair? Absolutely not, but it's the rule as written.

If it is 100% critical that you MUST perform your show, then do it pre-game or post-game. Don't plan on the other side giving you the time you need.