You may have to get a residence certificate from immigration. Every bank and branch has different requirements. You may have to visit several to find one that makes it less difficult. Or you could hire a person to do it for you. But that is getting more expensive every day. Best bet is visit a few banks and see what they require. Just avoid that one bank that is having issues
When i applied in May they said 14 working days and it was right about that time. If you had to provide more documents I would count 14 working days from the day you provided the requested documents. You can email them if its been longer. Start researching your options in case approval doesn't come in time.
to be honest, that one bank has been the only problem I've encountered so far in Thailand. It just happens to be a major problem. Very surprised the government or lawyers haven't done something. But I don't pretend to know Thai law. Just seems almost criminal whats been done to some account holders