Simone - there is a wealth of excellent and varied scenery within easy reach of Killin; I am trying to prepare an "information pack" for all participants which will give some details of our local landscapes etc, plus anything else which I find interesting and which is doable in a day. Many of the southern and central Highland's most famous locations are reachable from here - Rannoch Moor, Glen Etive, Glen Coe, Ben Nevis . . . the islands are, of course, wonderful but I doubt if any can be visited comfortably in a single day from Killin - you would have to spend one night there. All things are possible.
That's great!
I understand that an island would be a bit of a stretch to visit in one day. But one could maybe reach Arran which Google Maps says is about 4h from Killin. I could imagine leaving sometime after midnight to stay up and photograph sunrise and into the morning. Then maybe take a nap before returning in the early afternoon for lunch. I'm sure this would pay off if the weather is right. I don't know whether someone would be in for such an adventure. Staying there for one night is another option.
But I'm awaiting your infos, maybe there is something more interesting within an easier reach, e.g. a nice stretch of coast. I can spend hours at a nice spot with interesting rocks for instance, this is photographer heaven for me