I had some difficulty with this one, strangely enough. I don't want to cause panic by saying it's a glitchy achievement, but it is rather finicky. I tried crouching for 3+ minutes at a time in three matches, and it didn't pop. I had to stand at a far-off mounted turret with my Autosentry active for four minutes playing Big team Infinity Slayer on Vortex before I unlocked it.
Just keep trying, and most of all - be patient!
Edit: If you'd like to downvote this Solution, please leave a comment telling me what I should improve. Thanks!