Normally, especially since there are two accesses, the route closes an hour before the caravan passes by. Look at the timeline for the stage, which will tell you all of the times. It should be no problem. The other issue is not passage, but access to a space to watch - that often is gone at least a day in advance on the most popular climbs.
OTOH, it probably wouldn't hurt to contact the local tourist info office to be sure before you set out.