Booking Ski Passes in the Cairngorms

I'm renting a place in Aviemore over xmas and am hoping to get a sneaky ski in on boxing day afternoon and have been told that it will take about 1.30 hours to get to the ski slopes in the morning is that correct?

Also I have been told that I need to book in advance for my passes or i might not get on the slopes, that can't be true can it ?

any advice on what to expect would be appreciated