When you have homework, the easiest way to finish it is to finish it in chunks. When you want to eat healthy, you need to eat sparingly 5 times a day rather than 3. When people can't afford a car, they pay it off month after month until they've bought the car. If you want to run 20 miles in one day without getting too sore, you need to divide up your miles and spread them throughout the day.
As you can guess, today, I ran my 20 miles in chunks. I woke up in the morning and waited for my good friend Whitney to come down and run with me. We ran 3.01 miles in 30:12, an average of 10:02 min/mile, took a small break and walked a little, then ran 3.6 miles in 41:14, a 11:26 min/mile. After coming back, I ate a nice lunch, took a little break... and then went out and ran 9.17 miles in 1:13:58, an 8:03 min/mile pace. It was a little bit faster because I was enjoying the run and was working on making my legs move at a faster cadence. Then, after eating dinner, I took a little break... and then went out and ran 4.48 miles in 34:36, a 7:43 min/mile average.
It wasn't easy running it all in chunks, but it was easier than running it all at once. After each run, I ate something, so that my legs would get a boost into the quick recovery I wanted it to get in. My legs rested well enough, but at the same time, when I ran the later runs, I still felt the effects. The recovery time I had wasn't enough, but it helped build a stronger body that could continuously run with the soreness that would be part of running 50 miles.
Spreading out your workouts help make your metabolism stay high, it helps your body get physically fit faster because you're able to do more. Spreading out your life and your training helps each individual tremendously.