Time Is Stretchy?

Chemistry class:
I look at the clock. We've taken two pages of notes, and it feels like our hour-long period should be almost over. Lies. It's only been seventeen minutes. Class drags on forever, at least two hours by my internal clock, but the outer clock says it's only been an hour. How is this possible?

Spanish class:
A class I usually do not enjoy. The teacher is usually late, and today is no different. My internal clock is set to accommodate that. We're rolling right along, going through the homework, and I glance at the clock, thinking that it's been about fifteen minutes. Surprise surprise! It's been more than a half an hour! In a class that usually drags! Will wonders never cease.

Time is stretchy. That is my theory, stolen from Terry Pratchett. If you want to know more, read Thief of Time. It's an amazingly mind bending book, with monks, time travel, the Death of Rats, and Death's granddaughter (named Susan, thank you very much.) Oh yes, and a flying horse named Binky (owner: Death).