They hold in the rocks all day long, but with the recent warm waters, it's very tough getting them to hit, even after dark. If you can, use black or schoolbus Bombers, jigs, or flies after dark, casting parallel to the jetty from the sand. You can fish jetties during the day in the summer, but your chances of hooking up go way down if you're targetting stripers, and the amount of non-anglers or people-who-have-no-clue-about-anything exponentially increases during the sunlight hours. However, other species might be there, like fluke, blues, and kings, if you like them. If it's a bigger jetty, like an inlet jetty, fish from on top (if feasible and legal) at all different points. Don't discount the corner where the rocks meet the dry sand, either. I've caught the bulk of my fish off jetties right in those coves, where most people ignore them and head out to the end.