Mostly I agree with you about loading times, as long as the ship stays the same that will limit what can be done. Changing the ship though, that changes everything - compare the old fashioned way of doing things with dockers and cranes with a container ship.
The degree of mechanisation will be interesting, I can quite easily visualise a high TL planet where it is still done largely manually for any one of a myriad of social reasons whereas the next one along might have as much as possible mechanised. A good way of passing on local flavour.
Stealing from the real world the Liverpool dockers were notoriously militant and generally bolshie and once got embarrassment money for unloading a cargo of toilets. Apart from this cultural and religious factors can complicate things nicely - leave the PCs with a cargo of perishable Maguffin berries and dockers who will not touch them for religious reasons - nor allow anyone else to.
There was a story about a reefer whose refrigeration plant had failed mid-voyage with a cargo of Australian beef. By the time she docked the cargo was rotten and the ship stank - and the smell would not go away so the ship was eventually scuttled. An exaggeration I think but maybe something that could happen to the PCs, perhaps the hold stinks? One suspects that exposing it to vacuum for a while might cure this.
Stealing a story from my father some of the dockers might stowaway in the hold (let us hope it is pressurised). Depending on what he planet is like or when they are discovered they might be shot at the edge of the port hardstand or give a crewman a nasty shock. This leads into questions of what security and sensors are like for the ship and the ports, the former part of which certainly deserves it's own topic - and I think it has one somewhere here.
Long ago my father was a junior engineer on banana boats, fast reefer transports carrying bananas cross the Atlantic, fast enough to have run alone during the war with more important cargoes. A couple of stealable ideas:
Practical jokes. A hand of green bananas lifted from the chilled hold and kept behind a steam pipe in the engine room until nice and black then presented to the cargo master, telling him an entire hold was like that.
Whoops. A green engineer inspecting the hold collects a lot of bugs and spiders chilled and fallen to the deck when the cargo was chilled. In the hot engine room he opens the jar - and the revived insects and spiders boil out to become a curse in the bilges.
One week. Oh it is not a bad call for game purposes, it gives PCs a chance to wander around and get in trouble while still imposing a deadline.