This is a wonderful ferry and the timetable differs on different days. All the islands could be great to visit but you might like best to do the round trip of them all from Mallaig and back, which is possible on some days.
The islands are Rum, Eigg, Muck and Canna.
If you are at all prone to seasicness, avoid htis trip when there is a high swell!
The phone number is Calmac's mallaig office.