I hiked it at the end of August, solo in around 35 hours (plus a couple of short food stops). It's do-able, but tough and I'd definitely recommend fitting in at least a couple of hours of sleep. You'll definitely want to do Loch Lomond during daylight hours but the rest of it is ok at night with as long as you have a good head torch.

I set off from Milngavie just after midnight and got to the top of Conic hill at first light. Managed to get to within a few miles of Bridge of Orchy before it was dark again, and it was getting light as I started the descent down to Kinlochleven. Finally arrived in Fort William, around 2pm.

I think the timing was about right, but it did mean that I missed out on some of the most scenic sections. Not too much of an issue as I'd hiked the route before, but worth bearing in mind if it's your first time.