I'm following the Runners World training schedule for the autumn half-marathons - I'm doing the Windsor one on 29/09. I'm managing to do most of the training sessions and have done all the speedwork, but I still find that I need longer to recover between intervals than the schedule says I should take. E.g. on Tuesday I did 6 x 800m at 5K pace, and was supposed to take 60sec between, but needed more than two minutes each time in order to be able to complete the next 800m. Also I often stop and walk instead of jog. Does this matter? Is my speedwork not so effective?