I once arrived a few minutes late to meet a friend in Oxford and spent the walk there rehearsing an apology. Later, reading about Great Tom at Christ Church, I discovered the tradition of Oxford time, five minutes behind Greenwich Mean Time. I wished I had done my reading before the meeting.
I saved the page on my phone. Usually I forget historical details almost immediately, but this one seemed likely to come in handy.

Comic transcript
Panel 1. Nick arrives in Ben's kitchen. Ben stands beside a steaming saucepan.
Ben: “You're five minutes late.”
Panel 2. Nick raises a finger and offers his explanation.
Nick: “I'm on Oxford time.”
Nick: “Five minutes behind Greenwich.”
Panel 3. Nick holds up his phone, displaying a drawing of a bell. Ben looks down at the kitchen timer.
Nick: “It's a tradition.”
Panel 4. Ben points to the countdown timer, which reads 00:00. Nick's confidence fades.
Ben: “What time are the eggs on?”
Panel 5. Nick reaches towards the stove. Ben lifts an egg from the saucepan with a slotted spoon.
Nick: “Take them out.”