Overtime is cool, even if a jarhead did come up with the idea (Thanks Storm!).
It breaks down like this. Overtime simulates reinforcements coming in for the defenders. Once the battle has raged for a certain amount of time, more troops show up. So, once the overtime is reached during a mission, defenders are then supplied with reinforcements. A map time limit must be set for the mission to use Overtime settings. If no time limit is set, Overtime settings are disabled. When overtime kicks in, the extra reinforcements allow defenders out of lives to rejoin the action well. If you still have reinforcements left, you'll simply get the overtime additions tacked on.
Overtime Limit Percentage- This box determines the percentage of time remaining in the mission until the overtime reinforcements are sent in. If set to 50(%), then when the map time limit is half way over, reinforcements kick in. If set to 70(%), when 70% of the time limit for the map has elapsed, reinforcements kick in.
Startup Reinforcement Percentage- This value is the percentage of attacker respawns that defenders start out with initially. As it is usually more difficult to attack a defended position, this value typically creates an initial imbalance in the number of reinforcements each side gets, at least until overtime reinforcements arrive. For example, if this value is set to 75% and attackers begin with 4 respawns, then defenders will begin with 3. It's also fun to set this to 100% so they're evenly matched until the overtime reinforcements kick in.
Defender Reinforcement #- If the checkbox to the left of this field is checked then this value represents the number of reinforcements that defenders get in overtime. If the checkbox is unchecked, the default setting gives the defenders a full set of reinforcements in overtime. This means the initial amount of available reinforcements for the attackers will now be available for the defenders in addition to the reinforcements they still have remaining. I personally prefer to use the checkbox here and set the reinforcements to a low number, like 1 or 2. It adds a bit more tension that way.
Defender Delay- This value is the delay between when reinforcements are announced to be on the way and between when they actually arrive. So, if you have the overtime set to kick in after 50% of the map time limit has elapsed and the map has a time limit of 18 minutes and this value is set to 20 (seconds), reinforcements will arrive after 9 minutes and 20 seconds have elapsed in the round.
So, to sum everything up:
If you set the Overtime Limit Percentage to 80(%), the Startup Reinforcement Percentage to 100(%), check the box next to Defender Reinforcements and enter a value of 2 there, and set the Defender Delay to 30 (seconds), on a map with an 20 minute time limit, here's how things will play out if the attackers start with 3 reinforcements:
Both teams will start with 3 reinforcements (not counting their initial life of course). After 16 minutes (80%) have elapsed, a message will be displayed that reinforcements are on the way and all defender HUDs will update to show their new number of reinforcements (whatever they had +2). 30 seconds after that the reinforcements will actually arrive, allowing players who are out of reinforcements to now respawn.
I hope that all makes sense. We tried to give as many options for different settings and styles as we could but it can be a bit overwhelming at first I guess. Let me know if you have any more questions and I'll happily answer them to the best of my abilities.