Custom Map Makers

I have two sets of doors. I want the first set open and the second set closed for 6 minutes, then the second set open and the first set closed for 6 minutes, and so on. What is the best way to set this up?

The usefulness of this is to create an unbalanced CTF with 4 blue flags and 1 red flag for 6 minutes, followed by 4 red flags and 1 blue flag for 6 minutes.

Seems like you should be able to do this just by having one of the doors start open and the other doors start closed. Then just do a target delay / relay (whatever) to trigger both doors every 6 minutes. I don't know the precise entities for this off the top of my head but that's how you'd do it I think.