I'm really new to hammer and to making objectives. But, what if you made two flag poles or something and tied a button to each one with team filters applied to them? While Zombie flag is up, the human flag is down. As the timer runs out, it would depend on which button is currently depressed to determine the winner of the round. That might be easier than trying to have something that is based on which team is in the area as the timer runs out. Either way, I suspect you will have to research the 'logic' entities to make it work. Sorry it doesn't really help, but it might give you a new way to think about it.
In the brain and not the chest, head shots are the very best!
--ZOMCON-- A better life through containment.