If we wanted to close our lobby's on Saturdays, and just have the drive thru open, do we have to get approval from our regulator? Do we need to notify our customers by regulation or would that just be a customer service thing?

If you are State chartered, you need to check State law and regulation.

WE are regulated by the OCC.

Reduction of Services
A bank may alter the operations conducted at a branch without being subject to the branch closing requirements, provided that the facility remains a branch. For example, the branch’s hours of operation may be reduced, certain functions or services previously provided at that location may be eliminated, or a national bank branch may be downgraded to a night depository. Nevertheless, a bank should consider providing appropriate advance notice of service changes to customers as a good business practice even when statutory branch closing requirements are not applicable.

https://www.occ.treas.gov/publications/publications-by-type/licensing-manuals/pub-clm-bc.pdf

I looked for that on the OCC website - thank you very much. I need to refine my search skills I guess

Also don't forget to update your CRA Public File.

Thank you, Brian! That's a good reminder.