jjfluk
The vast majority of the freight flown by DHL, UPS, TNT etc goes at night. This fits in with the just-in-time principle followed by most of manufacturing industry.
DHL had a handful of daytime schedules a good few years ago but they didn't last too long. I guess in part that was due to staffing up for out-of-hours operations (not economic), crew FTL problems and difficulty with slots.
Most freight aircraft spend all of the daytime hours parked up, often in the less attractive parts of the airport!!