There isn't any standard; banks that use this technique usually just set the time frame based on the circumstances. However, 11 - 15 days is as good a standard as any. My suggestion is that a written policy on savings account holds simply say "up to XX days, unless a longer hold is approved by a supervisor."
My prejudice is that if I'm only willing to accept it for deposit into a savings account, I probably don't want to accept it at all. My desire to impose firm limitations on myself in that circumstance is weak.
My self-imposed burden would be that the customer would have to receive a written notice of the hold just as if the regulation applied.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.