This isn't nessesarily true. Time flies period, when you're talking months to years anyway. The last almost 4 years of my life have flown by and I've been doing nothing and been completely miserable.

If your talking about daily time however (minutes and hours), then its only if your occupied. I remember in bootcamp, we'd go PT for like 2 hours before morning chow, but it felt like it was more like 10 minutes. It was ANYTHING but fun, but damn it really went by fast.

So time (daytime) seems to fly faster based on how busy and occupied your time is...and years don't actually fly, they just seem to have when you look back...or atleast from my experiences.