OPDJ isn't always equal to DRQJ (Date requested), it depends wether you have TMS (transportation) active or not and also wether you have set up routes with transit and/or preparation days.
I would say OPDJ = PPDJ the first time you enter the order.
But JDE doesn't use this field from my experience, if you need to populate it manualy it shouldn't be a problem for the standards.
Fred