In my social circle, most invitations for dinner are fairly casual and "why don't you come for dinner?" means "come over for a meal and hang out afterwards for some unspecified period of time". In my experience, the "hang out afterwards" almost never involves watching TV or a movie; it's just more conversation. These gatherings most often happen on weekends so can easily run until midnight, which is about the point the first person says, "I'm tired and need to get going" and that usually triggers the rest to do the same. I think it would be difficult for anyone to actually overstay their welcome, because this is the way it's always been and it's what I expect on the occasions that DH and I are hosting.
FWIW, DH and I, and the majority of our social circle, are in our late 40's and early 50's, and most people either don't have children or the children are adults themselves. So that dynamic isn't a factor in determining what time we meet, what time we actually eat, and what time we call it a night and go home. And these dinners are not "dinner parties", really. Some are a litle more formal than others but they're all pretty relaxed. And whoever is hosting always provides some kind of snacks beforehand, or has made arrangements with one of the guests to bring snacks. There's usually something sweet afterwards, but not often a formal dessert. Maybe cookies or brownies with the after dinner coffee/drinks. Typically everyone brings something to drink, but that's more a courtesy than anything else, because the hosts always have enough food and drinks for everyone. There is the occasional exception, like a spontaneous end of summer BBQ that was specifically "BYOB".
On the relatively rare occasions that we host or are hosted for dinner on a week night, it does tend to be more "arrive at X time, eat dinner shortly afterwards, leave within an hour of dinner". But that's usually because the dinner part is incidental to something else; e.g.: "when you come over on Thursday night to drop off those things you got for me at Costco, stay for dinner; I'll make some of that spaghetti that you like."