Hi Kate -
It’s definitely driveable in a day. Maybe Richard, like me, has driven to/from Skye from/to Yorkshire in a fairly long day. Edinburgh however, should be a much shorter, more comfortable drive. I travelled with friends heading for Newcastle Upon Tyne via Edinburgh from Fort William and their route was Glencoe-Crianlarich-Callendar-Stirling-Edinburgh-Newcastle. (I think the excellent pie shop at Callendar may have been an ulterior motive! If you decided to break your journey, Callendar is a good stop off point). That said, no reason why you couldn’t follow the same route, taking the ferry from Skye to Mallaig, driving past Glenfinnan to Fort William. You could of course drive the whole way, but it will extend your drive time, but that said, the scenery is wonderful.
Ian