Hoover Dam is open daily from 5 a.m. to 9 p.m. (except for Thanksgiving and Christmas Day). Tours run from 9 a.m. to 5 p.m., with the last tour departing at 3:45 p.m. Lake Mead is open 24 hours a day, 7 days a week, 365 days a year. Some beaches and other facilities are open dawn until dusk. Check in advance here.