You won't find a prescribed period for responding to the customer's claim (please note the warranty applies equally to all customer checks, including consumer and business, including MMDA checks, HELOC and credit card checks) because the warranty in section 229.34(d) is strictly a interbank warranty.
The customer is not provided protection under that warranty, except to the extent that it enables the customer's bank to enter a warranty claim to recover funds for the customer. The customer's protection falls under the UCC -- if the customer didn't authorize the issuance of the check, the bank had no right to pay it.
That's a long way to go to get to the answer -- you should treat such a claim just as you would a claim of any other unauthorized paper item drawn on the customer's account.
Don't forget that, if you receive the item from the Fed, you have added protection as the paying bank under the Fed's special adjustment procedures for unauthorized remotely created checks.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8