I used to live in Scotland, so know the journey from down here well.
Its certainly do-able in a day to Fort William, but it would be a long day and you'd be knackered by the time you got to the really good scenary (everything north of Glasgow/Stirling.) You might also start to lose the light by that time as well, which would be a shame.
If your holiday time allows it, I'd recommend breaking the journey either in the Borders or maybe Stirling and then heading up to the Fort on the second day.
The best route for both scenary and twisty stuff is via Stirling, Callander, Crianlarich and Tyndrum. Glencoe is not to be missed in the daylight!
If you have time, the 50 or so miles from Spean Bridge to Kyle of Lochalsh is arguably the best in Scotland.
You'll have a great trip. Wish I was going too!