Assuming your flight leaves BKK at 12:10, you would want to be at the airport three hours earlier, at 9:10. If you were familiar with the airport and had status, you'd be okay with a shorter time, but leaving room for things to go wrong, I'd stick with three hours. Given that, I'd stay by the airport and go into town the first afternoon/evening for sightseeing and dinner. You will not get the very top luxury out there but there are suitable places to stay.