Just for interest for those who need to show 'a bank letter re funds' at Chiang Mai immigration yesterday there was a notice saying the official bank letter should be dated within seven days of the required visa renewal. There seems to be some confusion with certain people stating that it needs to be made within 24 hours or three days of renewal.
TLDR : Answer Summary
At Chiang Mai immigration, the official bank letter required for visa renewal should be dated within seven days of the renewal application. There is some confusion among applicants, with some believing it needs to be dated within 24 hours or three days.