Definitely worth searching the forum for this one, its been discussed a few times.
I tried (and failed) managing to get to Kingshouse in 12 hours having started at 5am in Milngavie. In my defence, the weather had been rotten most of the way, but I bailed mostly out of mince-ness, the rain coming over the top of the Devil’s Staircase was mostly horizontal…
Dmoffit on here has done it, as did some guy from Mull (north to south, but still a silly fast time like 11 hours or something) and of course Rob Lee managed Milngavie to Ft Bill and back to Kinlochleven in one sitting.
I’d only consider going south to north, seems more traditional, but probably the harder direction (saving the big hills for miles 80-95..)
And if you skip the nasty bits on Loch Lomondside it doesn’t count! 😀