We have modeled our Reg DD disclosures regarding "payment of interest" based upon the Fed's sample in the Appendix.
It states "Interest begins to accrue no later than the business day we receive credit for the deposit of noncash items (i.e., checks)."

The Reg DD commentary makes reference to Reg CC (229.14) which states "A depositary bank shall begin to accrue interest or dividends on funds deposited in an interest-bearing account not later than the business day on which the depositary bank receives credit for the funds. For the purpose of this section, the depositary bank may--
(1) Rely on the availability schedule of its Federal Reserve Bank, Federal Home Loan Bank, or correspondent bank to determine the time credit is actually received;...."

Are they talking about customer Reg CC schedules, or is there a different schedule between the bank and the Fed?

If there is a schedule between the bank and the Fed, how do I know what that is?

Go to your federal reserve district bank's website, find the section that addresses correspondent services, and look for an "availability schedule".