9:00 AM until 5:00 PM MST. The Visitor Center, park trails and viewpoints of the canyon are not accessable outside of the hours of operation.
Access to the Island Trail closes at 4:00 PM, and access to the Rim Trail closes at 4:30 PM.
The park entrance road, trails, and the visitor center are open year round, except on December 25.
NOTE: Most of Arizona does not observe Daylight Savings Time. The state is on Mountain Standard Time year-round.