If 7 am then screen brightness 50%

This will set the screen brightness to optimal 50% at 7 am so that you don't have to increase and decrease screen brightness everyday. (This rule is useful for those who don't like automatic brightness changing brightness every few seconds due to changes in light)

If 7 pm then screen brightness 30%

This will set the device brightness to optimal 30% after 7 pm. No need to manually increase and decrease brightness everyday. See related rule for incresing brightness. (This rule is for those who don't like automatic brightness changing brightness every few seconds according to minor changes in light)