I've never waited longer than 5 minutes in inbound passport control in T2, even after getting off the rear of a DL widebody. Departing through T1, both before and after KE moved to T2, the waits tended to be quite a bit longer pre-move. Now, unless you leave on a super busy day, such as a Korean or Chinese holiday, the process doesn't take too long (at least much shorter than it was pre-move). I've learned to avoid flying out any day of a Korean holiday if I can help it.