Norovirus hits rcfe, no visitors for now. on average how long will it take virus to run its course?

A few days to weeks: Presumably RCFE means assisted living facility. Surprising to bar visitors because of norovirus. If "run its course" means a particular patient, usually 1-4 days. If you mean time for the outbreak to run its course, it depends mostly on effectiveness of control measures: isolation of affected residents, staff hygiene, hand washing, maybe finding and correcting a common source (can be difficult).