Immediately after five p.m. on the day of the election, the election board publicly shall open and canvass the ballots cast and shall declare the result of the canvass. A mail ballot may be counted only if the ballot is returned in the return identification envelope and is signed by the elector. The chairman shall wrap securely all lists, tally sheets, oaths and affirmations, and other documents relating to the progress of the election and shall deliver the same to the secretary of the board of directors of the district.