Making time for yourself!?

I am a college professor, and I spend oodles of time making lessons, grading papers, etc. outside of cl. I feel like I never have any time for myself, and when I try to make time, I feel guilty like I should be doing something more productive. I know that I need to make some "me time." When I don't take enough time for relaxation, I become slower and less efficient in my work. Any suggestions on how to set aside that extra time for myself each day?