Thanks for everyone's reply. I didn’t literally mean “all” but "most or some" of the flights on UA that seem to have less than 24-hour flight duration. Also, was having an issue with departing BKK with UA/ANA flights departing at 12AM Sunday. That totally blows my Saturday night.

I did see a favorable roundtrip flights on Emirates IAD-DXB-BKK. Also, will consider different routes but I initially was looking on UA/ANA IAD-NRT-BKK

I think booking a transfer and going straight to Pattaya, get a good night sleep and be as fresh as I can in the morning is the best option if a late night arrival time is chosen.

Again thanks everyone for your advise.