Max I have used my Generator once was 18 hours straight on gas. A China made by Angel, 6.5 KWA, ran without any hiccups, still strong after 880+ hours of sheer torture :D. Oil was always inspected after roughly 40-50 hours, then topped up if needed to ( China gen. mostly eat oil, branded ones do use little to none). Max change interval ( Hours) I would recommend is 60-70 hours.
Oil used was Total 20w50. Just keep in mind to clean air filter regularly, check spark plugs and the usual tappet adjustments if needed and it will serve you truthfully.