2 days
Mull needs its own night
The ferry from Oban while the morning is fresh, a night in Tobermory, and the distillery on the harbour.
Tobermory is a ferry from Oban, and a world away from a Fort William loop. Give it the night.
Day one. Cross from Oban while you are still fresh. Walk Tobermory harbour, the painted waterfront beside the distillery. Boats, a wander, an ice cream if the shop is open. Sleep on Mull. The return sailing deserves the same respect as a flight.
Day two. Tobermory Distillery is the visit, best saved until you are already on the island and in no rush for a boat. Book it. The ferry has missed people with better excuses.
If the sailing home is tight, the harbour is still a grand day. The boat will not wait while you finish a story.