Yosemite National Park is open 24 hours per day, 365 days per year, and no reservations are required to visit. However, the Hetch Hetchy Entrance Station is open only during daylight hours (approximately) and some roads are closed due to snow from around November through May or June. (Check road conditions and Hetch Hetchy hours.)
Is there a best time to visit Yosemite? It depends what you're looking for, and each season has its advantages. Learn more about Yosemite in summer, fall, winter, or spring, and find out what kind of weather to expect.