Time management skills: How do I develop my sense of time awareness?

I've had a problem with time management for as long as I can remember, and a lot of it comes down to not realizing that time is actually passing. I often get so absorbed in completing a reading or writing a paragraph to my satisfaction that I don't realize that, you know, two hours has passed and I'm only halfway done with something that would've taken most people an hour. (This can be great in that I understand certain material really well, but I often don't have enough time/energy to complete these tasks and thus lose the benefit of understanding the overall picture.) Another common scenario is that I'll get so lost in an activity that I end up running late.