When should I apply for the COVID-19 amnesty extension on my tourist visa in Thailand?

It's not a visa amnesty which was completely different this is a visa extension

I'm *ASSUMING* you entered on a tourist visa or a visa exempt:

>Now I'm in Chiang Mai, where we hope to stay longer term

As long as your hotel filed a TM30, you can use Chiang Mai immigration office. WHICH office you will use, I don't know off the top of my head :(

>I understand they take the passport and you have to go back in 2 weeks?

Close. You will take your passport, and the required documents, to the immigration office. They will put an "under consideration" stamp, telling you to return between 1 to 3 weeks (or more). The date to return would be stamped on your "under consideration" stamp..

They *WILL NOT* take or keep your passport.

>I don't want to go too early because I've also read the extension starts the day you apply,

That depends on the immigration office, sadly :(

>I've also read the CM office says not to apply until 1 week before the visa expires.

That *might* be true. The extension you are getting is called an "Extension of Stay based on Unable to Travel Due to COVID-19", which technically is an optional stamp that an immigration officer may refuse to give. I don't know what their policy is exactly.

>Any advice on WHEN to go to immigration for the COVID amnesty extension would be greatly appreciated!

I'd go a few days before your existing stamp expires

For the documents to bring, I suggest bringing the following:

1. Your passport and:

a. a copy of your data ("picture") page

b. a copy of your most recent visa (if you have one)

c. a copy of your most recent stamp

d. a copy of your departure card

2. A TM30, filed in the immigration office.

3. The forms (each immigration office may have different forms)

4. A letter from your embassy saying you can not return, OR a print out from your embassy saying they don’t issue the letters.

5. 2x passport pictures

6. 1,900 THB.