How long does the marriage visa extension process take in Thailand and can I travel during it?

If you want to leave Thailand during your consideration period you should clear up with your immigration about a home visit by them

So you will enter on a single entry 90 day Non-O visa that you get from a thai consulate in your country.

Then as you need to travel during those 90 days you said you will buy a multiple re-entry permit at the immigration office here OR at the airport when you leave (keep in mind the re-entry permit will be valid only for the 90 days you get stamped in for, but it will let you exit/re-enter without losing that 90 day stamp).

When you have 30 days or less left on your current 90 day stamp you would apply not for a marriage visa 😮 (as you already have the Non-O visa) you would be applying for a yearly extension of stay for 1900baht

Once you apply you will get a 30 day under consideration stamp. You CAN leave the country on this stamp BUT you need a new re-entry permit (which is valid only for that 30 day stamp).

It goes without saying you have to be back in country by the time that 30 day stamp expires because you show up at the immigration office on that date and get the year extension inked in

And no, you don't surrender your passport at all, you hold it thru the whole process. You will need to coordinate with them if they are going to do a home visit during the 30 day under consideration stamp and your travel plans.