I will soon be cancelling my current Non-Imm Type B visa/re-entry.    My new job will commence a few weeks after the cancellation so I will leave the country temporarily.

How many days after cancellation am I granted before I must leave or be fined overstay?

You have to leave the country on the same day your extension is canceled unless you apply for a extension, pay the 1900 baht fee and be granted 7 days to leave the country after it is denied.

You can though go to immigration a few days before the day shown on a termination letter from your employer and they will post date the cancelation to that day.

If your current Non-B is BOI through the One-Stop at Charmjuree they give you 7 days grace after cancelling your visa. You can go get the cancel stamp up to 2 weeks before. Example go on July 18th to cancel visa. They will stamp cancelled as of July 31 and must leave the country by August 6th.     

9 minutes ago, RBOP said:

If your current Non-B is BOI through the One-Stop at Charmjuree they give you 7 days grace after cancelling your visa. You can go get the cancel stamp up to 2 weeks before. Example go on July 18th to cancel visa. They will stamp cancelled as of July 31 and must leave the country by August 6th.     

Yes it is indeed One Stop Chamchuree.  That's excellent news, thank you so much !

2 minutes ago, drbrit said:

Yes it is indeed One Stop Chamchuree.  That's excellent news, thank you so much !

Your welcome. Also note you need to do the online cancel notification a couple days ahead of going in. I'm going through the process now but letting the company agent do all the notification stuff. They also should cancel your work permit or you'll have an issue when applying for a new one. 

2 hours ago, RBOP said:

Your welcome. Also note you need to do the online cancel notification a couple days ahead of going in. I'm going through the process now but letting the company agent do all the notification stuff. They also should cancel your work permit or you'll have an issue when applying for a new one. 

OK, noted, thanks for the great guidance.