Day zero is the day before the ride. Many final "get ready" activities will take place.  Final pledge tallies, tent assignments, bike checkouts, and the like.  More information here as it happens.  Standing in lots of long lines.  Watching a mandatory safety video.  Getting the required wrist band showing that I saw the safety video.  It goes on for hours.  Nobody will say for sure how long it takes. 

Find out about the 

Opening Ceremony!