I ran my 5600w 8k surge BS powered Craftsman eleven days straight without an oil change in the hurricane Sandy aftermath. Just a level check and top off if needed. After power came back it got an oil change with Walmart SuperTech Full Synthetic 5w30 it had in it and back into storage for the next time. It ran quite a few more 1-2 day events afterwards getting oil changes before storage until I sold it last year as it was no longer needed in my new place with a Generac standby unit.
Zero issues with that 20 yr. old generator other than replacing its electric start battery.
Cold starting a 0f or lower temp. unit, 0-30w oil is your friend, experience there on a recoil start same size gen. set.
Do not cheap out on a miserable quart of oil, put a good synth. in it for long, dependable engine life.
Good oil and fuel, or at least properly treated E10 fuels, will never let you down. I store with treated E0 gas myself.