coach travel to Saalbach or Munich

Does anyone know how long it takes a coach to travel from Calais to either of these two places. Trying to work out when we need to cross the channel to make sure we hit the resort around 2 or 3pm. Want to be able to book a ferry that will make sure that happens. By the way its a double decker coach so maybe a mite slower than the singles, and its gonna have 55 schoolkids on board as well as a few adults. Had one estimate of 17 hours to Saalbach
Cheers