Originally Posted by
Thai-Kiwi
Frankly, I'd depart CNX earlier in the day and grab a hotel in Bangkok or near the airport......
This is solid advice. I would also fly to BKK earlier and buy a cheap hotel in the vicinity of the airport (often rates as low as 1,000 THB/nt). Then go to bed early and wake up for a shortly before 4AM check-in with QR.
Sorry, I misread the OP concerning the CNX-BKK fare. Even with a fare difference of THB 1,800 I would buy the ticket for Y/M rather than J.