Great advice - it's way to easy to spend hours without letting your eyes rest. We tend to neglect the important part of our body that allows us to make sense of the world and do our work - our very eyes!
One of my tricks is to look around clockwise and anti-clockwise, 4 times each ways, at different points of the day. And up and down, side to side. Keeps the muscles around the eyes healthy and alleviates strain, too!
A blue-filter feature on your computer screen is also essential!