You would have to apply for a non-o visa at immigration to get a 90 day stay and then apply for the one year extension.
The 400k baht only needs to be in the bank on the day you apply for the non-o visa.
See: https://www.immigration.go.th/wp-content/uploads/2022/02/6.FOR-PROVIDING-SUPPORT-TO-OR-BEING-A-DEPENDANT-OF-A-THAI-CITIZEN-SPOUSE-VISA-NON-O.pdf