For the timer, set a variable called game_timer, of type timer. At map initialization (or whenever the timer starts counting down), begin timing. If you want there to be a window on-screen saying what the timer is at, then you need to
Action: Create a Timer Window for (All players) showing game_timer.
Finally, you need a trigger to detect when the timer hits zero.
Events: A timer expires
Conditions: Expiring timer equal to game_timer
Actions: Set Victory flag for (All allies of <captain of team 2>)
Set Defeat flag for (All enemies of <captain of team 2>)