@Henrik ****
Not entirely accurate, I’m afraid.
When you enter Thailand you need a TM30 with at least 15 days on it. Show it at Bangkok immigration and they will issue the residence certificate.
I had only 7 days on my TM30 from the hotel and the lady at immigration showed me an English document detailing the 15 day requirement.
We went to the Isan village after 7 days so we decided to open the account there. I had an account after two days in the village (after registering a tm30 at the house of my sister in law).
You do *NOT* need to be 3 months in Thailand for the certificate!