This achievement is glitched, but you will love this glitch. Instead of hosting 20 hours of games, you only have to host about 3-5 hours worth of games. In order to do this, set up a game of one target devastation, and set the time to 30 minutes. Do this on Manor House. Just play the game quickly and blow the target up and no matter what the time is at, at the end of the game, it will count for 30 minutes.
Another way of getting this is when boosting the achievements, just make the time set at 30 minutes for every game, unless you are going for "Last Second Hero".
Note: You can not play 1 vs 1 ranked matches. Minimum is 3 vs 3!