What is the process and expected wait time for applying for a multi-entry visa at Bangkok international airport?

hello, gd morning from bkk.

I am about to apply for an extension for my retirement visa at bkk c.w. immigration office.

Thinking about whether I should apply for my multi entry visa on the same day but my worry is there may be loads of people who wanna apply for it in the same office. that being said it may take a long time.

my second option is to apply for it in my next departure from Thailand in the bkk international airport.

could anyone share their experience of applying for the multi entry visa at the airport?

about how long it takes to get one?

after getting the visa, will they give a departure stamp on my passport and then I can leave for the departure gates from the office or should I go back to the passport control counters as most others do?

Thank you for your time n reply.