It varies.
Here is cut and paste from a post in thread regards income method..,
"I applied for my retirement extension a few days ago, using the 65k method, at Jomtien Immigration.
They required me to show both the statement from the Thai bank (which, btw, took a week to get...no-one mentioned that part to me lol)...and also some proof of where the funds were coming *from*"
I suggest folk provide a 12 month bank statement.
True BBL take few days (5), however other banks on the spot.
You can obtain that day or two prior to attending immigration.
Cost: 200b