A pocket watch is displayed and proved to the audience that it does not work. A spectator is selected and shown that the watch hands spin when the stem is pulled, but that's all.
It is held to the spectator's ear, but as the watch is broken it does not tick and the hands don't move. The magician then announces that he is going to set a time on that watch between now and the approximate time his show ends, and then gives it to a spectator, informing them that at any time during the show, even if he is in the middle of another trick, to yell out, "Now is the time!"
At the most inopportune time in the show, the spectator calls out, "Now is the time!" The actual time is verified by the audience, and when the watch is opened it is seen to be set to that exact time.
