The fastest way to get this achievement is doing it in the
Party Bus level. Pick the hero who "may start massacre." He has a chainsaw and a special power where after pressing
he goes into a rampage mode and kills everyone close to him and moves incredibly fast too for a couple of seconds. After this he needs to recover his energy for another couple of seconds. Once you are in the level, simply activate that ability and kill as many people as possible. After he recovers, kill the rest of them. I have done this level in 4 seconds, so this achievement should not take you more than 2 minutes to complete after the three repetitions. Heck 1 minute seems like too much time too! :)
This method will also net you the following achievements if you do not have them yet:
The Runner achievement in Party Hard worth 112 pointsComplete level in 3 minutes