If we are talking a money market account, then giving a customer 10 business days before closing an account may be reasonable to ensure that any outstanding checks can clear. Also, if the account receives direct deposit of social security benefits, the Green Book requires that we give the customer 30 days.
Since in 25 years of banking I have yet to read an enforcement action that involves a Reg D violation, as an auditor, I'd be chasing higher risk fish than this.
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