This was actually a second part of the question that I was going to post. I wanted to first see where I would need to do immigration, and then ask about the visa on arrival. We're not going to have any bags (just carry on), and we should get boarding pass for the domestic (BKK to HKT) flight when we check into our first flight as both are on one ticket. We do have a little more than an hour between the two flights (6:50 am to 8:05 am), so I'm guessing this is going to be enough time for the Visa on Arrival process.