At any time after the closing of the polls and not later than the canvass of the voters cast at the regular voting places in the city at any election, the board of supervisors of elections shall proceed to count, certify, and canvass the ballots contained in the ballot envelopes, received prior to the closing of the polls on election day. All voter's applications, medical certificates, notarial affidavits, ballot envelopes and ballots shall be kept separate and apart from ballots cast at the regular voting places and retained for six (6) months after the date of election at which they were cast, unless prior to that time, the board of supervisors of elections shall be ordered by a court of competent jurisdiction, to keep the same for any longer period.