All ISTPs do it. You've got some chores you should do, a errand to run, a phone call to make. You put it off by thinking, "I'll just do it in five minutes." Then you get engrossed in some activity, you forget your chore, and you completely lose awareness of time passing.
For me, my computer is like a specialized time assassin. If I start surfing the web, I can and have killed 8-10 hours at a time. If I get engrossed in a computer game, I can and have gone from 5 pm to 11 am. In retrospect, horrifying. WHERE DID ALL THE TIME GO?!
On a smaller scale, I can take 30 minute hot showers. Eat a meal/read a newspaper for an hour. Wake up in the morning and lie in bed another 2 hours, dozing in and out and savoring the warm, soft, comfortable bed.
What's your ISTP time killer?