My distance is long enough that I need to change from distance to time. My weekly goals for time are 1 hour, 1.33 hours, and 1.66 hours, representing a rest run, a medium run, and a long run. It takes me about an hour to do the 2.8 miles, so I think I'm ready to start using time instead of distance. The advantage of time is that for the same time, the distance covered varies according to how the runner feels, and this change is automatic. I'll start using time and then increase the mid and long runs a bit as I get stronger, until I reach my goal for the three times. I'll keep the rest run the same time as today. I run 3 times per week, and that allows me to do all three times each week.
I've been running 30 seconds and walking 50 seconds, but I changed to 35 seconds and 55 seconds earlier this week. These changes are small, especially for younger runners, but they work fine for older runners like me. I like Jeff Galloway's run/walk method. It allows me to go further than I would go if I did no walking. When I was younger, though, I would do only running. I later learned about the run/walk method and changed to it.