You're making me nervous.
Regulation DD cross references Reg CC at 229.14 regarding when funds must begin to earn interest. In essence, if you are going to delay interest accrual until you have good funds, it must be based on your institution's actual clearing arrangements, not an arbitrary time frame. Regulation CC dates back to 1988. In the intervening years the clearing system has accelerated. Moreover, your bank may have changed its actual clearing arrangements.
So, even a valid, documented calculation of average collection times has a limited life expectancy.
_________________________
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.