Traveling Scotland by train and bus. Any tips?

Hello everyone! I'll be travelling around Scotland in October, and I'm considering using the Spirit of Scotland pass. I would need some clarification on how it works. When I buy the 8 out of 15 days pass, how are the 8 days of usage defined? Does it automatically deduct a day every time you start using a transportation service, showing the pass the first time for that day? Or do you need to indicate in advance the 8 days you have the intention to use it within the 15 days of validity?

Furthermore, I see on the map that the bus route from Inverness to Fort William is included, but I can't find any stops in between available in the check service section of the site. Does anyone know if it is possible to go from Inverness to Urquhart Castle by bus with this pass?

Thank you!