The first week is about slowly building up time on your legs again. Not about how much running you do. Following the run walk is critical process to follow so you can slowly build back up the amount of time you run. The process seems slow but before you know it you will be up and running again.
Week 2 we slowly increase the run time on your legs but keep the overall duration similar to week 1 so we don"t overload the muscles. Its all about small steps forward rather than big steps forwards only for problem to return and 2 step back.
Week 3 we are starting to get back to running now. Our body should be slowly getting stronger and muscle use to spending time on legs. We can increase the load so we are running more than walking but still want total duration the same as first 2 week. We don"t want to increase run duration and overall duration at the same time otherwise it can cause a overload on the body.