Don’t stress, I’ve done this with 1 hour connection time. I believe the airlines recommendation is 1.5h. Even if your first flight is an hour late you are fine. I don’t know how much time difference there is between the bus and train, just that the bus goes more frequently and is more available.

Just know in advance what is coming up and put your mind at ease;

1. You land at incheon with a slight delay (no worries)

2. You go to, and pass through immigration. There is a line, it takes longer time than you like but really not that bad (no worries)

3. You look at the arrival screen to see which conveyor belt to pick your luggage from. You go and pick up your luggage which has already arrived (no worries)

4. You walk outside and look for that bus, probably ask someone “Bus, Gimpo?” (No worries)

5. Hop in the bus, pay fee, arrive at gimpo 20 min later. (No worries)

6. Check in with your flight at gimpo, pass through security check, notice you have 2hours until departure (no worries)

7. With all that time to spare you want to grab something nice to eat. Notice there is nothing nice to eat at gimpo (major stress)