A prophecy about an event we agree will happen is only meaningful if it forecasts a precise time to watch for the event. 

Suppose I make this prediction: "the Eiffel Tower will collapse some day. Watch for this event." Such a prediction is meaningless because eventually the Eiffel Tower will collapse if we wait long enough. We agree it will happen some day--the Tower won't remain forever. The only question is when it will fall. The prophecy is meaningless because we believe it can happen at "any moment."  Now, assume I predict the Tower will collapse on an “October 13 date in the future, but the year is unknown.” The prophecy becomes meaningful because people now know precisely when to watch every year. 

This is the problem with Bible prophecy about the return of Christ or end of the world.  Any prediction about the return of Christ or an event preceding it is only meaningful if it foretells a precise time to watch for it.  I discuss this in The Millennium Chronology.