I first thought of Top 5 Comedies over 2 hours, but Comedy is such a broad definition, which can be mixed with drama or other genres to give you something like Forrest Gump or The Apartment.
I'm looking for long films that remain laugh riots through to the end.
My Top 5:
1. The Blues Brothers
2. Love Exposure
4. Operation Petticoat
5. Victor Victoria
6. Midnight Run
Love Actually would make the list with some debate. It's a comedy front to back and the end has some of the funniest scenes, but there's also a fair bit of drama wedged inside. Similar to Parenthood, but Parenthood's a superior film and it gets in because of that.