Most schools require you to work five days a week. Some will require you to work six. That said, in order to make ends meet, many teachers in Thailand "freelance" and teach private students on the side.
If you want to do this, it is possible to burn yourself out by working 7 days a week. It's up to you really - and the lifestyle you want to be able to afford.
The work is out there, it is just a matter of whether or not you want to take it all on.