It usually depends on location, nearby activities, and my personal financial situation at the time. If I really need to conserve cash, I might consider working exorbitant hours.
If I don't need the money, I won't work more than 20 hrs/wk for the site. Even that is stretching it some. Has to be a very nice park - pool, nice sites, reliable wifi, etc.
If the park is within a couple miles of a prime paddling spot or near my grandkids, I'll consider working more as long as I still have enough time to enjoy myself.
Personally, I've turned down some trashy parks that wanted 25 hrs/wk just for site.