Please find more info about 20-20-20 rule from the below links.
http://www.optometrytimes.com/editors-choice-opt/deconstructing-20-20-20-rule-digital-eye-strain
https://opto.ca/health-library/the-20-20-20-rule
https://www.healthline.com/health/eye-health/20-20-20-rule#definition
Optional Step :
In order to not to get error while installing application you have to export root CA file.
https://knowledge.digicert.com/solution/SO13755.html
Follow the above steps with "Sridharan.cer" file.
This script is designed in such a way to follow 20-20-20 rule.
Run "ProtectYourEyes.exe" when you are start working. This will alert by playing an alarm tone for the configured time(Default 20 minutes).
Time is configurable meaning you can set the default time for yourself. (Ex: 15 minutes)
When you are done just close this application.