Cal. Water Code § 50705

The polls shall be kept open from 10 a.m. of the day of election until 4 p.m. Where the real property in the district is assessed to 500 or more different individual, joint, or corporate owners, the board may elect to keep the polls open from 7 a.m. of the day of election until 7 p.m. and in that event shall include the time of polling in the notice as provided in Section 50732. However, when the board holds an election which does not involve added costs to any other local governmental entity, the board may elect to keep the polls open from 7 a.m. of the day of election until 8 p.m. and in that event shall include the time of polling in the notice as provided in Section 50732.