On the front page of the Runner's World web site, they have introduced a new personalized coaching program. (So why did I get my USATF Level 1 Certification?)
I input 24:20 as my recent 5K time.
It was the time for the recent run as a workout as part of my recovery plan.
Selected a 5K as the race I am preparing for.
I do mostly 5K's as they are popular but will run from the 5K up to the half marathon.
Selected 11-15 miles as what I currently do.
Which is a little more than I am at now, but less than I normally run (20-25/week).
Selected the "moderate' level of effort for training.
Clearly the "middle of the road approach, but for grins, let's see.
It came back quickly with a 16 week plan of workouts mostly following the 3-day FIRST plan but for several weeks adding a fourth day (Friday) with some easy runs.
So this tool should be good to use. I would skip the 4th day and up the effort on the other days to compensate.
Try it out. See what the wizard says for your inputs. If you want to review that with me, let me know.
May the roads/trails be kind to you!