Emergency generators normally are 3,600 rpm units. Those are NOT designed to run for long periods of time.
If by chance you have an 1,800 rpm unit those MAY be usable for longer periods of time before voiding the warranty.
The best unit IMO is a Hawkpower unit that has a Lister Petter diesel with the internals modified to burn natural gas. Those you can run 24/7 for about six weeks w/o voiding the warranty. With the large capacity oil pan you can double that run time.
IIRC those engines are good for 40,000 hours before a rebuild,
Right those Hawkpower ones are industrial generators. Maybe costing near $100K or more.