Do we need to inform our regulators that we are moving our cut-off time for accepting checks back by one hour?

As you know, Regulation CC requires you to notify your customers at least thirty days prior to implementing any change that shortens your availability policy. 12 CFR 229.18(e). However, the regulation does not require you to notify your primary regulator of the change. We are not aware of any OTS or OCC requirements apart from expectations that you comply with Reg. CC.