You are offered a choice between two experience machines.
Machine A is just like the ones you already know about. You’ll be on the experience machine until you are 120 years old, getting lots of various sorts of pleasure.
Machine B offers exactly the same experiences as Machine A. However, the experiences are crammed into a much shorter period of time: just one day. The first 12 hours of this day seem to last 12 hours. The next 6 hours seem to last 12 hours. The next 3 hours seem to last 12 hours. And so on (as in Sorensen’s "The Cheated God"). A fraction of a second before the 24 hours are up, the machine kills you painlessly. At that time it seems to you as if you have lived 120 highly pleasant years.
Which machine should you choose?
It seems to me that a hedonist should be indifferent between these two machines. Life on one is experientially indistinguishable from life on the other. But suppose we attempted to get an objective measure of the amount of pleasure you get in each machine. The pleasures in Machine A last a lot longer than the pleasures in Machine B. So objectively speaking, Machine A offers more pleasure.
I guess some hedonists might prefer Machine A. But the example at least shows that there should be two ways for a hedonist to account for duration. An "objective hedonist" would look at the actual durations of pleasures, in absolute time. A "subjective hedonist" would look at how long the pleasures last in the personal time of the subject. I think more needs to be said about how to formulate hedonism in terms of personal time, but I thought I’d throw the idea out there and see what people think.