I got a 3 entry tourist visa. Now I am on second entry to Thailand. I know it's possible to extend a tourist visa, but can I extend the 2nd entry? If so, how many days would that be?

I have in mind to change my tourist visa to a non-immigrant B visa. Would an extension give my enough days to get the paperwork done to do so? Application for work permit is underway since last week.

You can extend any entry and the period would be 30 days.

Normally a change of visa status inside Thailand should be started with 21 days remaining but this has not been a firm requirement lately so believe you may be able to get it done.

If you plan to use the 3rd entry you must watch the expiry date of the visa stamp itself (usually 6 months from issue)

and make sure you get back to Thailand on or before that date