There are three distinct walks on Out Skerries, which Alltrails calls 1) Bruray Circular, 2) Bruray & Housay and 3) South Mills Circular plus combinations of them. Although a Sunday daytrip leaves time for all three, a Friday trip will need to sacrifice one of them. Other days of the week are impossible due to the Vidlin ferry timetable. Any thoughts if I'd prefer the Friday trip?
Have you found the Out Skerries walk on the Walk Highlands website? This website is usually regarded as the 'Bible' for walks in Scotland. Looking at it, it seems to combine all three of the Alltrails routes. It is desceribed as: distance 11.75km / 7.25 miles Time: 3.5 - 5 hours
I look at the site. We'll only have 3 hours, so I need to pick and choose (or walk faster).
That's not going to give very long - the Out Skerries are flat so distance views across the islands are good. The coast is more interesting than the interior. I think I'd begin with the harbour area and walk out towards the airstrip on Bruray and then retrace steps to Housay and do part of that loop, depending on how time goes. Look out for the remains of the old field systems near Housay.
Based on last summer's ferry timetable, a day trip is only possible on Friday with 3.5 hrs on shore and Sunday with 7 hrs on shore. I think 3.5 hrs leaves time to do the Bruray loop and one of either the South Mills or Housay Circular.s. If the terrain is similar it probably doesn't matter.