Join Date: Mar 2009
Location: Chapel Hill, NC
They can go home the moment the first rider rides the prologue in most situations. Once the field is set, no additions or substitutions can be made. I can recall a couple situations where riders were injured the morning of the start of the race and substitutions were made that morning - and there are great stories of riders being seeded to start last for their team in prologues after team injuries or illnesses. They get called up and travel last minute, many times arriving just minutes before their prologue start times.
All the grand tours have rules and have an established date and time for the roster to be set. Sometimes this is the day before at team presentations, other times its just prior to the start of the prologue on the first day.
They also go home as they won't have places to stay. Usually the GTs provide barely enough rooms for the riders and 6-8 support staff per team bunking double occupancy in the tour lodgings.