Rory has a nightmarish bus journey back to Hartford, which begins with the bus unable to even leave the terminus, as an accident has temporarily closed the interstate. We don’t get much of an idea as to how long that took, but in such cases, the interstate is usually closed for at least an hour or two (sometimes more than a day).
Rory sends Lorelai a pager message to say that she’s been held up, and will try to get to the ceremony by seven, but might be later than that. This sounds as if the bus was delayed from starting for more than an hour. It’s annoying, but Rory can still make the graduation ceremony at this point, even if she misses the first part of it.
The problem is that she soon discovers to her dismay that the bus is making many stops on the way back to Hartford – she caught an express bus in the morning that went directly to New York, but this is a local bus service which picks up passengers and lets them off along the entire route, meaning travel time is much longer.
In real life, buses are often delayed or take longer routes, something Rory may not have known but probably should, since she catches an intercity bus every day to school. Reviews for the New York to Hartford bus service complain of lengthy delays, often taking four hours to arrive, so this is a believable situation. If Rory was delayed from starting by two hours, and the trip took four hours, she might not be getting into Hartford until somewhere between 8 and 9 pm.
Note that Rory’s backpack on the seat beside her looks remarkably flat and empty – did she throw all her school textbooks away while she was in New York???