Laws of Cricket 1947 Code - Law 18
The Umpires shall call "Time", and at the same time remove the bails from both wickets, on the cessation of play before any arranged interval, at the end of each day's play, and at the conclusion of the match. An "Over" shall always be started if "Time" has not been reached, and shall be completed unless a batsman is "Out" or "Retires" within 2 minutes of the completion of any period of play, but the "Over" in progress at the close of play on the final day of a match shall be completed at the request of either Captain, even if a wicket fall after "Time" has been reached.
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