This was in October, 2022. It took them a couple of months to get to my application. Once they started looking at it then it took a couple of weeks to get the approval. I scheduled an appointment at the BOI office in Bangkok. They finished a few more documents and then walked me over to the immigration office across the hall. There Immigration cancelled my OA visa and entered the ink stamps for my LTR. I paid the 50,000 baht that day in the Immigration office.
I went to the BOI website and used their online application. I should say that my finances are simple. I qualify for the pensioner LTR with a single work pension. I submitted my US 1040 tax return. It shows that I have only two sources of income - work pension + Social Security. They never questioned my finances. I already had an insurance policy to maintain my OA visa. I uploaded the same insurance certificate that I used for my OA visa extensions. I uploaded a copy of my passport.
You should come on a long stay visa such as an O, OA, OX, LTR, or Elite. If you enter on a tourist visa or DTV you will probably not be able to open an account.