Time Based Training Trial Run

I have never followed a time based training schedule, so I wasn't quite sure what to make of the time based schedule that the TNT coaches recommended we follow to train for our races.  I was concerned that their schedule wouldn't be the best fit for me and ultimately I decided not to follow it.

Just for kicks I decided to give a time based run a try during a recent long run.  My regular schedule called for me to run 8 miles and the time schedule called for me to run for 75 minutes.  I ended up running 5.93 miles in just over 75 minutes.  Not quite the 8 that I was supposed to run, now was it?

The run reinforced my main concern about the time schedule: I am much too slow of a runner to follow one.

On this particular run, I ended up about 2 miles short. What happens when I've followed this schedule while training all season and by the end I'm falling 8 or 10 miles short on my long runs? I know I haven't yet made it to run a full marathon yet, but something tells me 26.2 miles is going to hurt if the longest I've ever made it prior to the race is 16 or 18 miles.

I also felt totally unmotivated during the run.  All I was doing was watching the clock tick along knowing that I had to keep running until it hit 75 minutes.  There was zero motivation to try to run faster since it wouldn't help me finish any quicker.  In fact, I found myself giving in to my exhaustion and allowing myself to slow down a lot more than I would have if I was running toward a mileage goal.

All in all, the trial run reinforced what I was pretty sure I already knew - time based training is just not for me.