My father has a number of flights of over 16 hrs in his logbook, all complted in a Mk2 Shack. One involved a diversion from Labuan to Singapore due to WX at Lab.
On a personal note, I have 6 flights of over 12 hrs in various gliders. One is 13.50 in a failed attempt to fly from France to S Italy. Nimbus 3. Last month flew AUH - ORD around 16 hrs as a pax.
However, the longest I have ever seen entered in a logbook was a flight of 46 (?) hrs in a Catalina/PBY 17. The owner of the logbook was an ex RAF AG who explained that they had been patrolling beteen Iceland and Norway and landed in a fiord a couple of times to refuel from drums stocked on shore. Kudos.