June 10th for Simi, Conejo (Thousand Oaks), and Pleasant Valley (Camarillo). Moorpark is out this Friday (June 3rd - would have been the 10th, but they have the last week as furlough days apparently). Oxnard and Ventura are June 16th.
Summer hours start today (Memorial Day) and end on Labor Day. That's probably the best way to gauge expected crowds. Lots of schools take end of year trips, so that adds to the crowds even before the kids get out of school. They'll probably (hopefully) clear out somewhat early in the evening though.