Bangkok bank 1 year statement takes around 5 days (Chiang Mai)for them to produce, the bank letter is valid for 7 days and you have to update your bank book on the day, so I go at least a week before and order the statement then go to the bank on the day to pick up statement and the letter and update my book, you can pick up statement and letter a few days before but must update your book on the day you go to immigration
Just go to immigration with all your required documents, I think the online site you are looking at just check your documents are correct, but you still need to go to immigration and pay the 1900baht fee.
the letter/certificate lasts for 7 days, most people go to the bank on the day to pick up year statement, letter/certificate and update bank book. Bank book must be updated on the day you go to immigration.