It's not the total length important. The gaps between the work is important.
During computer work there is reduced in blink rate. That make ur eyes more exposed and dry. And there is the main culprit dryness.
Health Tips
1. Use 20:20 schedule. 20min work with 20sec relaxation, by watching far objects, washing face with regular tap water.
2. keep ur desk top below ur eye level, to keep ur eyes half closed.
3. every two hours of work followed by lubricant eye drops.