Da Voismart Knowledge Base.
Says a specified time in a custom format

  unixtime: time, in seconds since Jan 1, 1970.  May be negative.
              defaults to now.
  timezone: timezone, see /usr/share/zoneinfo for a list.
              defaults to machine default.
  format:   a format the time is to be said in.  See voicemail.conf.
              defaults to "ABdY 'digits/at' IMp"