Rode the Great Glen Way from Inverness to Fort William in a day, against a strong head wind. Took about 9 hours in total, including stops for coffees and lunch. No food outlets between Aberchalder and Banavie, so make sure you have your our supplies. Met several people en-route who thought one day to complete was a bit much, for an average rider 2 to 3 days would be a more comfortable pace, but the route is easily achievable in a day especially if you have the wind behind you and not carrying any luggage.
Believe Nevis Cycles rent bikes at the Fort William end for one way hires. If you want bed and breakfast near the Fort William end, look up Torcastle Bed and Breakfast, just outside Banavie and on the Great Glen Way route.
Look out for the Garden Cafe at Aberchalder (next to the swing bridge), great for lunch or a snack and hot drinks.