When does one need to apply for an extension of stay on an STV visa in Thailand?

Hopefully you are not seeking to obtain a teaching job at this time in Thailand. As the STV visa cannot be changed into any other visa inside Thailand.

30th

Your good until June 30th

Because I'm sure it'll come up, here's a recent report about getting a 90 day extension of stay based on STV from Nonthaburi Immigration:

"I was in Nonthaburi to extend my STV visa. Here's what the officer asked...

1. Copy of passport

2. Copy of TM6

3. Copy of STV visa page on your passport

4. TM7, use the last updated one or get it from Immigration Office. With a photo affixed.

5. STM 2. Declaration that you're aware about overstay and the penalties.

6. ASQ certificate letter stating that you've completed 14 days quarantine.

7. Some kind of proof that you indeed stayed at the ASQ, i produced my ASQ hotel receipt ( room charges )

8. Health Insurance showing coverage amount, line by line items in details of IP, OP, Covid coverage amount.

9. Rental. To state clearly rental period when to when, at where, 4 signatures either passport or Thai ID at the end of agreement ( the usual standard contract ). If the rental's address is in Bangkok, you can only extend visa in Bangkok. Rental period should cover at least 3 months more.

And sign at every page."

I'm also attaching a screenshot from an e-mail from Bangkok Immigration explaining what they want for a 90 day extension of stay based on STV.

The visa sticker is valid for a certain amount of time (90 days generally). For the STV, you have 90 days from the time it's in the passport to the time you can enter Thailand.

When you enter Thailand, for an STV, you are stamped in for 90 days, and you can stay up to the "admitted to" stamp (the red inked bottom page).

You can apply for a 90 day extension of stay based on STV when you have 30 days (45 days at some immigration offices) remaining on your existing admitted to stamp.

You can apply for a 90 day extension of stay based on STV at around June 1, 2021.