Probably not a lot but it wouldn't be uncommon for an American plane to be in the air for 12+ hours with in-air refueling.
According to references, 13.5 hours [0] is the record for the F-16 combat mission, and this was actually a SEAD (Suppression of Enemy Air Defenses) mission in a single-seat F-16CJ. Similar missions in the EA-18G extended to 13+ hours with a single pilot, along with a WSO/EWO in the back seat.
Various unofficial reports indicate F-16s do fly 14 hour ferry flights, but that is highly unusual.
At the Evergreen Air & Space museum (home of the Spruce Goose), they have an old SR-71 on display. Part of the exhibit has a TV playing a video loop with pilots and crew talking about their experiences. One of the pilots recalls how they'd have a "high-protein, low-residue" breakfast like steak & eggs before a long mission. The idea was to provide long lasting energy without having to go "number two" in the suit. He says that some of the crew who would help them out of the flight suit at the end of a mission were female, so it'd be especially embarrassing if you'd pooped yourself. I got the impression that, while rare, it did happen sometimes. :-\
(2 + 2 + 2 + 2 + 12) / 5 = 4.
And so on. This whole statement is meaningless without more information about the distribution of lengths of flights.