How long it will run depends on what your fuel supply is like. As long as you have enough propane (or whatever it is running off of), you can run indefinitely.

I've had a general for 12 years now. The biggest thing of late (fortunately it doesn't affect me) is that Generac has gotten very proprietary about things (they've encrypted their monitor port on the later updates of the firmware to bar third-party monitoring solutions and personally, theirs sucks badly).

Mine is on a 1000 gallon propane tank (no natural gas here). Running for three days didn't really even put much of a dent in the tank.

The only limit I see is that the engine needs an oil and filter change every 200 operating hours.

Propane or gasoline?

I have a smaller propane generator, your model may burn 10 gal of propane an hour.

I pay over $3/gal delivered.

Thanks everyone! Its a 22 Generec on natural gas. Thanks for the tip for 200 hours. I ran this past the sales person before signing on the dotted line. Now we wait many many wks.