Answer:
If you are aiming for the midnight deadline and don't have a forgery affidavit yet, return the check for a different reason that doesn't require the customer's affidavit. Code L - Signature irregular is a likely candidate. Making that midnight deadline means you retain control and don't have to rely on the depositary bank's response to a bank-to-bank "without entry" warranty claim.
If you've missed the midnight deadline, wait for the affidavit and use the without entry warranty claim route.