Best time to have surgery: Morning (4x less likely to have complications in the morning than between 3-4PM)
Best time to get a human being on the phone when calling a company's customer service line: As early as possible (lowest call volume)
Best day of the week to eat dinner out: Tuesday (freshest food, no crowds)
Best day to fly: Saturday (fewer flights means fewer delays, shorter lines, less stress)
Best time to fly: Noon (varies but pilots say airport rush hours coincide with workday rush hours)
Best time to exercise: 6-8PM (body temp highest, peak time for strength and flexibility)
Best time to have sex: 10PM-1AM (skin sensitivity is highest in late evening)
The nuggets are from Mark Di Vincenzo's Buy Ketchup in May and Fly at Noon: A Guide to the Best Time to Buy This, Do That and Go There which I expect the fun-facts-at-cocktail-parties crowd is buying by the bucketload. The pointer is from Barking Up the Wrong Tree, via Andy McKenzie.
Note that the worst time to do anything is immediately after lunch.