From what I understood there are two main Muslim "centers of influence" in France: the Grande Mosquée de Paris (the main Mosque in Paris) and the Conseil Français du Culte Musulman. From what I understood, this "Conseil" decided it should start yesterday (Tuesday) while the Mosque said it should start today (Wednesday). Finally they all agreed that it should start today.
I have no idea how they can't just set a date worlwide and stick to it, or at least discuss about it sometime BEFORE they actually think it should start (because some french muslims already started yesterday due to the confusion).