Inverness is a better datum. Sunset at 1933BST, twilight at 2012BST. Official night 2003BST. You could probably add on a few minutes since the crash area is West of Inverness but it would not make a lot of difference materially.
The AIRMET for the area was pretty bad with high winds, heavy rain, low cloud, hill fog, and poor visibility forecast.
A needless tragedy.