When can I fill out the DTAC form after arriving in Thailand?

You can do it day before you depart-

The TDAC is not a visa. The electronic TDAC is just replacing the former TM6 arrival & departure paper card you used to fill out aboard your flight before you entered Thailand.

You can fill out and submit the TDAC (Thailand Digital Arrival Card) starting three days/72 hours before your planned entry; it only takes five minutes on your home computer, it takes a little bit longer on the smartphone

Every non-Thai citizen is required to have completed the TDAC, regardless of whether they have a visa or an existing stay permit.

It's important not to fall for fraudulent websites that charge a fee for the TDAC—they're all scammers. The official TDAC is free of charge.

Open the official website and simply fill it out pro forma.

Create a note or a Word .doc document on your computer with the requested information, e.g., passport number, name and address in your home country, primary address in Thailand, and so on.

Then, starting up from three days/72 hours before your planned entry, you can copy and paste the information into the TDAC—it only takes two minutes!

NOTE: The "Visa Number" and "Departure" from Thailand are NOT required fields; you can leave them blank.

BUT: As soon as you click on one of these fields not marked with a red *asterisk or start typing, an error message will appear if you don't fill out anything else. Then you would have to cancel everything and start over.

The TDAC confirmation will reach your email inbox shortly after you have submitted the form. You should print out this email confirmation, as it contains a QR-code. Mainly expats who apply every year for their annual “extension of stay permit”, should print it out, because a printed and signed copy of the TDAC could be a part of the document submission on Immigration

If you don't have to present the printed TDAC at the immigration counter, it doesn't mean anything - the border official will see the TDAC you submitted on his/her computer screen as soon as they scan your passport, so they won't ask again

The TDAC is not a visa, it is only an information you give Thai authorities about your person, your arrival information and your place of stay.

Assuming you haven't completed a TDAC, they won't let you enter the country but will send you back to the terminals in front of the Immigration desks with a request to submit it.

If it's too early it will just not work, so you will know...

Michael you could have filled the tdac in already by the time you spent on this post.

Asia Pacific time

Correct, from 72 hours before arrival it is possible. And since you also have to enter the flight number, it is understandable.

On line 3 days.

If you can count back from zero ( time you land) to 72 that's your answer.

Fill it in any time within the 72 hours of arriving in front of immigration. Just count back. You can even do it waiting to board, when on the plane, or on landing. Up to you.

You will notice