In reply to ablackett:
Hi, I actually followed that plan in 2017 (I'd been running around 50km/week easy-medium pace before starting that training), and it was going quite well, I ran a 1:26 HM with about 8 weeks to go, on a tricky course, and also felt good a week later when I ran a solid 20 slow + 12 MP:
https://www.strava.com/activities/1174597544
Then I got injured, with about 7 weeks to go. I tried some pool running, and the occasional attempt at a proper run, but the training regime went out the window and I lost my motivation.
By the time the marathon came round I was ok again and I ran it in 3:11. I could really feel that I'd missed the high mileage training runs.
I'm not sure I would have made sub-3, I'd also had some issues earlier in the program.
I did add on the occasional easy pace long run, and I also raced the local weekly short trail race. I think it was the intensity of the training and trail races that broke me. Running 3:45 - 4min/km on undulating trails with tired legs from the other training was too much for me.
The reality for me is that I've been fully renovating a house the past 3 years (which is why I tried the shortcut training plan), and in the winter my priority is ski mountaineering, so I don't have the "time" to supplement running with good strength and flexibility training. I have recurring ankle, achilles, knee and hip problems. I've put the sub-3 marathon on the back burner and currently just do easy trail running until my house is finished (this summer) and I can replace time spent renovating the house with renovating me.
I plan to try again in 2020, I'll start this summer (14 weeks was too tight and left no margin for injury/illness) and replace the yassoo 800s with intervals of 2km. I liked the fast medium distance and the long distance with fast end, but by having a longer lead up to the marathon it's easier to postpone an intense session if my body isn't feeling it. I will also mix in some cycling and strength work.
I've never tried a fast 5k or 10k, but I don't think I could go under 18min for the 5k without specific training.
The sensible advice would be that 5 months is too short from your starting point, and it's probably better to target 2020, but who wants to listen to sensible advice!