The campground we frequent has gen hours of 8 am to 8 pm, and the rule on the noisy "construction" generators, is that they "can only be run for short periods". That is vague, yes, but I have seen the rangers get on people who ran them for several hours, and then they only ran them less than an hour at a time. Another campground we go to, noisy generators are prohibited completely.
I have seen campgrounds with hours of only 3 or 4 hours for generator running. It varies so much, you need to check the rules at each place.