I've at the most left it on for a week. Other than that daily shutdowns when I go to bed. My laptop sleeps most of the time so maybe a month on the laptop.
I've actually started shutting down my workstation here nightly, but at home just turn the monitors off at night - and restart periodically - maybe once a week.
That may be good advice, especially when our electric provider is asking for another 18% hike in fees this year again. Unfortunately, I run security cameras across the Internet, so shutting them down is not possible.