I found this old thread from 2012 in which there is a picture of a document which was being handed out by Chonburi Jomtien Immigration at that time.

In paragraph 4 it says “ a letter from a Thai bank not more than one week old “. Does this still apply today or has it changed since 2012? I'm sure I can remember reading the letter from the bank can only be the same day as the application is lodged?

http://www.thaivisa.com/forum/topic/568687-documents-required-for-extension-of-stayretirement/

Most places a day or two before is accepted. But they do want an update of the bank book on the date of application.

Asiantravel, hello,

As I went to the immigration department at 8:30 in the morning, I make a bank letter yesterday as well as copies of my bank book with the stamp of the bank. I've never had to worry.

Do not forget to bring the original passbook.