You can either do this at your own pace online or with a second controller. Select Scavenge and then play with friends. While the game is searching press to create a lobby, then start the game with a single round.
Once you start playing you can just sit and let the timer run out. Make sure you move out of the safe zone to start the timer. You don't need to win to unlock this achievement, you just have to take part in five games from start to finish.
If you set more than one round you will have to play through however many rounds for it to count as a single game.