When Does a Tourist Visa Extension Start in Thailand After September 26, 2020?

30 days from 26 September, I think so.

Please read the first words of point 1.

Short term visa holders (TS, TV, VOA) and those granted a visa exemption have to prepare for departing the Kingdom within September 26, 2020.

I would say start preparing and take care your belongings if you live in Thailand for long time and did use these short term visa.

It might be you can not come back the same day with new tourist visa.

Stop putting your energy in how can i maximize and squeeze as many days out of this stay,

You can go anytime before sept 26th and if they agree to give a visa because you have a valid reason your extension will start on sept 27th. You don’t have to leave it till the end of September they want you to go before that to avoid crowding

Number 2 is for long term visa, so tourists visa enter in point 1. I think as wrote 🤔

The notice does say "ALL types of visa....." so it would be fair to assume this includes tourist visas, otherwise all tourist visa holders will be queuing up on Sept 26, which is exactly want immigration want to avoid. I guess the easiest solution is to rock up there and ask before you hand over your dosh

It is my understanding that all extension of stays will be effective the day after the amnesty expires. So, the last day you can stay in Thailand is September 26 + however long your extension is (30 days in your case)