Provincial Parks throughout Nova Scotia are open from May to October, and they permit those who are not registered as campers to enter as late as 10:00 PM (but you must leave by 10:30 PM). The smaller day-use parks that you might stumble upon, typically have their gates open from dawn to dusk. Please keep in mind that only campgrounds allow for overnight camping.
For more information on general rules and regulations, please visit the Nova Scotia Provincial Parks website.