, sadly, that information is very incorrect. As you can see in the PDF file from the link I provided, you need to show the bank letter about your account with 800K baht for an initial in-country visa application.
, basically, yes, you have to do them in 15 days as Bangkok requires you to have the remaining 15 days with your stamp when you apply for an in-country Non-O visa. You can add a 30-day tourism extension if you need days.
Or getting SETV from there entering for 60 days (+ 30 days tourism extension)
Getting a bank account as a tourist is not impossible but getting difficult. You might need to try dozens of branches. (Unfortunately, opening a bank account is out of the scope of this group.
There are some embassies such as Vientiane, Phnom Penh, and a few others that are supposed to issue Non-O retirement. Check them if you want.
Or, you can apply for Non-O based on retirement in your home country or neighbouring countries to enter Thailand on it and be stamped for 90 days. Then transfer your funds immediately to be seasoned for two months when you apply for a 1-year extension around the end of your 90 days on retirement.
Unfortunately, you need your bank account BEFORE you apply for an in-country Non-O visa based on being over 50 at the local immigration office.
Bangkok doesn't require you to have your funds seasoned for in-country initial Non-O visa application. You can apply for a visa next day of your deposit. Two months of seasoning is the requirement for a 1-year extension application when you already Non-O (90 days) stamp.
Bangkok requires you to have a lease agreement for application for an in-country visa and following 1-year extension
Attachment is the rough process for visa and extension applications all inside Thailand.
This is the requirement list for an initial in-country Non-O visa based on being over 50. But you need to get the latest one at the CW office.
, off the rails a bit. As long as you withdraw or deposit money after 0:00 tonight (anyway of internet/mobile/atm) the date record would be 6 March. Then update passbook anywhere (pum) before heading to CW in the morning. Just a thought.
, because, usually, under-consideration period is the first part of the new extension, not starting on the day of application. In OP's case, U/C starts 26 April (it 25 April is the expiry date).