My permit to stay expires September 30, 2022. Can I book a flight for October 1, 2AM? Will I be stamped and charged overstay fees?

You will likely go through Immigration before Midnight.

 

 

I can't imagine that you are sweating a 500 Baht payment.

There is no fine for a one day overstay.

You might get a small stamp in your passport but it would give you no problems.

11 hours ago, hotandsticky said:

 

 

 

I can't imagine that you are sweating a 500 Baht payment.

Reminds me of the old days at DM Airport watching tourists scrabble around for 500B to exit.

3 hours ago, QballQ said:

Reminds me of the old days at DM Airport watching tourists scrabble around for 500B to exit.

When you had to pay airport tax yourself, rather than it being included in your fare? Yes, that caught out a few people. There have been rumblings that something similar may be returning, with a special charge at the airport for arriving tourists. That proposed charge has been postponed several times as there are concerns about the effect on tourism.