I learned the trick of making a particular playlist (or three) and being able to judge the time by the song playing. I felt it was much easier to just know by a song then by posting several clocks around the room and visually checking those during a session. Anywho...whenever I did FBSMs I would often lose track of time (usually by over-exaggerating how much time had passed). I used my playlists to help me out most in those times, BUT...but, I'd get bored of the music and after a busy day I'd be sick of it all.
I dreamed of offering a 20% discount to clients who would let me listen to NPR during a session, but I never put it to paper. I mean, it's not a bad thing, really. Ira Glass gets me hot, so it's less work for you!