Definitely NOT the gunner littlebird
Just the regular littlebird, police and civilian/luxury helicopters
(But maybe the co-pilots of the gunner littlebird and blackhawks could be good because that would give them a reason to exist)
I'd say make it 12 seconds like recon drones, or at least 8 seconds like the recon class standard pings
That would make it so that you can use the helicopters to scout out enemies from above to help your whole team push or defend objectives
And it would have barely any chance of being OP because the player doing it can't do anything to capitalise on it themselves. If none of your teammates are in position to kill them then nothing will come of it