I sent an in-game ticket about this but I'm fairly sure that was an inappropriate use of the in-game service (sorry!).
But, anyways, the 5 targets you need to defeat in the mission only spawn one at a time, and those spawns only happen in two places. To add to that there is a very long re-spawn timer for each group, which ended with 8+ people all vying to get the first hit on either of the 2 spawn points.
In my experience it took 30+ minutes to defeat the 5 targets while grouped with 2 other people, most of which was due to waiting around for them to spawn.