I'm not sure I agree with the idea of deliberately delaying stuff? Surely what they must be doing is literally prioritising packing... They have 5865 prime orders and the system delivers those orders to the packers first, then after they have completed their prime packing, their to do list becomes normal orders, so perhaps they get to that at the end of the day and get less done and thus it takes days?
Also, say they were packing a normal order, then a prime order comes in, their computer system then jumps the prime order to the front of queue, again further delaying a normal order etc and so on.....
This makes more sense to me and explains everyones story, and maybe it's especially busy at times when ordered causing huge delay sometimes for normal orders where other days there might be v few prime orders and so normal orders may leave same day?