Like someone else mentioned, that is for street cleaning. Check the JC Parking Twitter for days that street cleaning is suspended. However, they only give tickets if you are there when the street cleaner comes and are in the way. So, if people see it pass or know it already did, they will park back on the street. Technically they could ticket you if you’re there between the times, but I’ve only seen them do it when the street cleaner is about to come by, if that makes sense.