Well, FedEx is the same as UPS in this category, if they get volume in a day early and it is in time to make their preload sort (the sort where the volume gets placed onto the vehicles) then they will try and deliver it early. It's actually cheaper for the company to get the package out of the building early than keep it there for the actual delivery day. Also there are less chances for mistakes, the systems are just not designed to age volume on site, they are designed to get it out as soon as possible
-spike