Why are the bails taken-off from the stumps at the break time & end of the day of a Test-match?
According to Law 16.2, 16.3:
The bowler’s end umpire shall call Time when the ball is dead on the cessation of play before any interval or interruption and at the conclusion of the match. After the call of Time, the bails shall be removed from both wickets.
So, this is the official way to show that the match has been paused or finished.