I take it you guys are on your own bikes, and not on one bike ? I also assume you guys have already accomodation/stuff planned for the Friday night in Edinburgh (down the docks.. :-) )
We're camping above you, about half way up Loch Ness and then left down Glen Affric. Where we'll be riding out to on the Saturday will largely depend on the weather, we'll be chasing whatever sun there is. I could imagine a loop, returning through Glen Shiel (Bruce?). That would be close-ish to where you are planning to be.
But, obviously, you're more than welcome to come along Friday pm, and you could do your planned route on the way back to Edinburgh on the Saturday ?
not sure yet, but I had hope to leave Friday late-afternoon. that would give 3 or 4 hours of light. what time suits you ?