Time telling in Thai can be tricky. The informal way to tell time (which is what you will probably hear more often in Thailand), uses different words for each hour!
I hope these table and diagram with color can help you. Plus, I have included a little historical explanation on the time system! :D
So.. What time is it now? ตอนนี้กี่โมงแล้ว? (dtāawn níi gìi mōong láaew)