Time is a complicated phenomenon, and this is grossly simplifying things, but the gist here is this: Anything that takes you out of the moment will make the minutes feel like they’re passing more quickly. Pre-planning every last moment of your trip is nice, in a way, because it lets you go on autopilot; you don’t have to make a decision about what to do on the second afternoon of your trip, because you already know you’ve booked a harbor cruise (or whatever).
Leaving room for spontaneity, on the other hand, means you have to think each moment through. Should you go for a walk, or have another beer? These are the important decisions that plant you firmly in the here and the now, and that makes for a trip that seems to last just a little bit longer. Alas, when on vacation – if you’re not careful – time works in the opposite way that it seems to on Tuesdays.