As a programmer all the thing that we just need for programming are relax and fresh mind condition. So with the good mind condition, we can do programming well.
Can you do programming intensively in 3 hours..?
Like doing a study 3 hours is long enough to make our mind tired. So Sometimes it's best to walk away, and come back to it later fresh. Then you'll notice those things.
All people need refreshing, not only programmers. Refreshing activity is important to refresh energy/stamina and mind.