P&T's camo takes 2 seconds to activate and as far as I've been able to see, lasts until you stop looking down the scope or once you fire. So I don't think there's a timer that needs stacking. Just keep looking down sight.
EDIT: After using it a bit longer I found that the camo does have a timer. Something like 20-30 seconds maybe.
English
-
I'm probably going to buy it just for the lolz :p ...and the fact that Xur isn't selling any Hunter helmets besides the gunslinger one...
-
It lasts a minute as a hunter, which is crazy lol
-
P&T active camo does ware off If you look down the sight too long