An early start, say 4 or 5 am, is definitely the way forward. The first section from Milngavie is steady away on wide tracks. Conic Hill is a carry up as the track is worn away by water running down it. Take the descent that goes off to the right as opposed to the main path down – much more fun.
Balmaha to Rowardennan is surprisingly up and downy in places with fireroad then tech until Inversnaid.
The advice to do the carry when it is light is sound.
Good on you for doing it. If the weather is grim, you’ll come to appreciate waterproof trousers and mudguards! Oh and Alpikit dry bags are a very good thing too. There’s nothing quite as nice as having dry gloves, base layer and a hat to change into when you get to the stage of feeling you’ve been riding in a shower for several hours. For me, having treats like jelly babies or a bottle of coke in the bag are always good as a pick me up mid ride when you are miles from shops. For pure energy food, Halva is really hard to beat for it’s small size. 😉
Good luck and post a report when you do it!
Cheers
Sanny