From what people were reporting in the Phuket sandbox it was generally less than 6 hours from test to result, but Bangkok might be another story.
I think until a few weeks have passed and we see it working in action we won't know.
If you're landing next week and don't have time to wait to find out, i would prepare for the possibility of extending to a second night or see what fees might apply to late check-out after 12pm.
to be safe maybe pick a hotel that has partnered with a major hospital for testing and is close in proximity, confirm with the hotel they will be able to test at midnight or 1am when you arrive, find out what the latest checkout possible is before you need to book a second night.