Most aircraft have 5 minutes of WEP with a 10 minute cooldown time (WEP can be restarted during the cooldown, you just get 1 second of WEP for every 2 seconds it spent cooling).
Bf109F-4 and later German aircraft have 10 minutes of WEP with a 10 minute cooldown time (WEP can be restarted during the cooldown, you just get 1 second of WEP for every 1 second it spent cooling).
The Ki-84 has 90 seconds WEP with a 45 second cooldown (WEP can be restarted during the cooldown, you just get 2 seconds of WEP for every 1 second it spent cooling)
The A6M2, A6M5, Me163, Me262, Yak-9T, Yak-9U and, IIRC, P-40B and F4F-4 do not have WEP.