For train times use the smart phone app national train enquiries, far more user friendly than Scotrail or any of the train operators own websites. use the planner section and it gives train times for 12 weeks in advance. It also gives platform numbers (not really necessary for the west highland line though
) Also has live trains section which has up to date times delays etc.
Its a free app on android phones, not sure about iphones. If you don't use a smartphone there is a national rail enquiries website also.
Had a quick look for 4th January . There is a train leaving Fort William at 0830, 1212, 1619 & 2214 with a journey time of about half an hour to Glenfinnan.
All the best.