We often leave the camper hooked up, particularly when we camp and go the next morning, though we usually ask for a pull through so there is room for the truck. If there is no truck room then we have to unhitch.
Depending on how late it is, we eat outside, then watch the news, sleep, make breakfast and then head out. It is no different than stopping at a rest stop to eat lunch in the TT.
If we arrive late where we are going to stay for a few days, dark or not, we setup. At least we unhitch, level front to back, (most camp sites are okay side to side for us), hook up the electric and enjoy what is left of the evening around the picnic table. We leave the water and sewer hook-up until morning in case it was not as level as it appeared the night before. ;)