You have to make a deposit or withdrawal in order for the bank book to update to present day. Every year when I apply for extension of stay I do a small deposit like 100b and re-run the book to get a current date and balance.
As stated above, you need a 2-month statement (I do 3 months just to be sure) - but you also need a guarantor letter signed by the branch manager or someone of sufficient authority. These can be done up to 7 days before you apply for the extension. Also, you will need to update your bank book on *the same day* of your application, so before going to immigration deposit 100 baht and update the book to show current 400k+ balance.
Conflicting reports last couple days, need to clarify. Guy here says he went yesterday and it's open. Would seem ridiculous to close down such a successful and popular service.