Jesus makes clear that the exact moment of the Son of Man's coming is not certain. Whether he is referring to the destruction of Jerusalem or to his ultimate coming to bring time to an end is not so clear. To me, it seems fairly clear that while there will be very obvious signs of Jerusalem's imminent destruction, Jesus' return is incalculable. In fact, he tells his disciples three different stories to help them understand that they cannot know the exact time of his coming. He, himself, does not know the time of his own coming. Neither do the angels. The bigger issue is the surprise and unexpectedness of his arrival. It will seem like any ordinary day with eating and drinking and marrying going on just like in ordinary times. No one will be expecting it. But his disciples will be ready for it. It may be a surprise but they won't be unprepared!