Just adding a small addition here, because I've been struggling to get this achieve. When you choose Game Lab it will search for a session, looking for about 15 seconds each on a map before looking for another. If you're like me, after about 2 minutes it will bring up a prompt saying "Unable to find session. Search Again?" (or similar). If this happens choose no, as it will change the game type from Game Lab. I didn't find this out until after I had played 5 games with the achieve 'glitched'.