Asia - How long for ICN departure immigration/security these days?

I am transiting through Incheon on Sunday and want to go outside the secure area for a while to meet up with a friend while I wait for my next flight. I remember when ICN was newer there were frequent complaints about long waits to get through departure immigration and security lines. Has this improved any?

How long should I expect on a Sunday evening? (8pm departure)

Also are there any special lines for Prestige class or business class passengers or does everyone queue together?

Couple of entrances, each entrance usually has two lines/machines working for security, shouldn't take more than 10 min.

Immigration usually moves fairly efficiently - another 10 minutes, even if jammed, won't be more than 15-20 max. Incheon is quite efficient.

Lots of good food places, shopping, etc. once you get back in.