How can I "automatically" get a reminder that day is done?
Go to the built-in Clock app and add an alarm for the time you want to go home or log off your computer. Select repeat and choose the weekdays that you want it to go off. You can choose a ringtone or song (We Gotta Get Out Of This Place) instead of one of the standard tones if you want.

The Timer tab in the Clock app can sound an alarm after 8 hours if that's what you want instead.