Open throughout the year. High Route trails can be closed due to bad weather; all trails can be affected by maintenance activity.
Need to Know
It is hilly! A mountain bike is ideal, but a hybrid or rugged road bike would be ok with high volume grippy tires and low gears. The High Route paths are steep, narrow and loose-surfaced, but well worth the effort.
Weather here can change quickly, so carry good waterproofs and warm clothes (it rains here regularly, and can be windy). In warm, calm weather there are likely to be problems with midges; they are less of a problem in early Spring and late Autumn.
For our trip, we left our car in Inverness and used the 'bike-taxi' from an Inverness-based company Ticket to Ride to carry us and our bikes from Fort William back to Inverness after the ride. Very effective, and well priced. They also offer baggage transfer, if you're prepared to pay to ride lighter.
Based on the trails before and after this alternative section, I anticipate that the alternative trail will include sections of undulating gravel forestry tracks, singletrack, and/or doubletrack paths through the woods.
Note that this alternative section still involves climbing!