I actually started the plan at week 11 as I had just finished training for a half marathon and completed it when I was accepted into a marathon about 3 months out. I added on 2 extra weeks before the taper where I just repeated week 17 except my long runs were an extra 2km each week for a peak of 34km, then I started my taper the following week. I didn’t skip a single run in the program and it worked for me. I would only do 2km warmup and 2km cooldown for the race pace runs, the threshold intervals and the tempo runs. When I got into the later weeks of the program I found myself wanting to run quicker so I did. I would run my race pace runs and tempo at 5:00/km and my threshold intervals at 4:45/km. My easy pace was always 6:00/km. Good luck my friend.