Originally Posted by Daxiuyi

Plenty of time, assuming you can check your bags through (should be ok).

When you get off the plane at ICN, follow the signs to transit security (it'll be early, so shouldn't be much of a queue). Go through security, up the escalator and you're in the main terminal. Then just look for the signs to the concourse (where your Thai flight will depart from) and take the shuttle out there. Shouldn't take more than 30 mins (especially at that time of the morning).

I would recommend hanging out in the main terminal (more to see/do) and going out the concourse at the last minute; there isn't much to do out there and once you're there you can't go back.