When lowering advance limits on Ready Reserve accounts is a 30 or 45 day customer advance notice required?

You are going to have to define a Ready Reserve account?

Open end credit attached to a checking account

Advance limits are a contractual issue and not a Regulation Z disclosure requirement on a consumer open-end credit account. You will need to refer to your contract for change of terms requirements.

However, if the actual amount of credit available to the borrower decreases, an adverse action notice is required.