Thanks Bob, I eventually found that I could "Delete" the unwanted plug from the "Scene", so things are now working as I wanted them to! :D
Regarding the possibility of a lack of support for the WooxHome App due to the company going into administration, I don't know if it is now possible in IFTTT or the Smart home app to use "Sunset at my location" as a valid trigger for an action.
I seem to recall that at the time, only the Woox home App would accept either Sunrise or Sunset along with the geolocation as a "dynamic trigger".
It was the deciding factor in my purchase so hopefully the other Apps will by now have caught up and offer this fairly basic facility.