Depends on the generator. I'm very conservative and I use nothing but 5w40 HDEO oil in all of my engines.
Aircooled high rpm (3600 rpm) generator with no oil filter, I'd change interval at 50 hours.
Aircooled inverter generator with no oil filter, I'd change interval at 100 hours or 2 weeks use whichever is longer. I had no problem running 2 weeks between oil changes running my generator 6-8 hours a day.
Water cooled and/or generators with oil filters, I'm comfortable with 150 to 200 hour intervals with a high quality synthetic HDEO.
In Afghanistan, our diesel generators ran 24 hours a day and were shut down one a week for about 30 minutes for the oil and filter to be change which amounted to about an oil change every 167 hours or so.