This challenge just have you to defeat a certain numbers of waves under the time limit. You will be fighting these waves in one area unlike the 'Runner' achievement (see below). If you do not beat the challenge under the given time you will not receive the achievement.
*You can create a match with just 2 people to start, you can choose up to 4 players.
Note: Must complete all challenges under the given time, and with the exact amount goals to receive the achievement for the given challenge!