Montrachet is a champagne yeast, so it will dry your cider out pretty quickly. If you want a sweeter cider, I would suggest letting it do so, then allowing your cider to clear in primary or secondary for a while (maybe a couple weeks to a month), then back-sweeten and prime with sugar and apple juice, bottle and pasteurize as soon as carbonation reaches the level you want. To simply say "pasteurize after 3 weeks" means you will have a basement full of shrapnel and sticky appley mess.
Back off man! I'm a Scientist.