@Don ********
@Kool ******
is correct that Chaeng Watthana will accept bank letters up to a week old, as long as the bank book is updated on the day of application. That's in their written instructions, and is also my personal experience - I got my bank letter a day or two ahead of time for my last several extensions. I don't know about Jomtien, though, which is where the OP plans to apply.