Okay, couple things.
1. Both because you have limited time and because you're a masters runner, and because you're an American: Focus on the quality way more than the quantity. I forget the name, but one of the top masters marathoners did double days of progressive 5x1000m reps (nearly) every day, where the middle one was about at race pace. That takes a very particular mindset, of course, but I agree with the principle that you need to have a very high percentage of your training (obviously you need to build up to it) around your race pace, with some significantly faster as well. If you're structured about your quality, I don't think you need more than 50-60 minutes daily. I don't know if your goal is possible, but you won't know until you try for real. You clearly haven't come close to giving yourself a real shot in the last few years.
2. You might do well to start off a minor resistance training program. Mostly because compared to what you're doing and used to, a single stride at the pace you're hoping to run (5 flat) sounds like it's a pretty strong muscular contraction for you. So, lunges, squats, kettlebell swings, planks, etc.
3. The real problem with this letsrun idea is that I'm not going to go into trying to justify or explain any of this more than whatever I just did, and I think part of coaching that's important is that the athlete understands why he does something.
Anyway, good luck.