What is tete de la course? And why are they at the front of the pack leading the peleton by quite a high time margin? And who decides the riders to be at tete de la course? And I think everybody at Tour de France should start at the same, it isn't fair for a pack to start early than the rest of the riders?
Tete de la course is French for head of the course, and means the front of the race that day.
All riders start at the same time each day, and their time to complete the course is accumulated to decide who wins.
On different days different riders decide to break away and try for the stage win, or more realistically to improve their profile within a team, or advertise their sponsor more effectively. These riders simply pedal faster than the others, and if a few work together and the peleton don't actively chase, they can gain quite an advantage.
If a team in the peleton decides to chase, however, most breaks will be caught.
Tactically a break may succeed if nobody in the group poses a threat to the race leader or one of the jersey holders, but if they do the break will be chased down. This has resulted in riders being ejected from a breakaway as they will cause the peleton to chase the break down!