For case-by-case holds, any notice that's not given at the time of the deposit is pretty much useless to the customer unless you have some way better than snail mail to provide the notice. In fact, the Fed's Reg CC proposal would make impossible to impose a case-by-case hold other than at the time of the deposit, if the customer has given you an email address for notice purposes, unless you make the notification by email no later than the business day after the day of deposit.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8