Hey,
good timing. I did this ride on Saturday. I rode from Hepburn Springs to Castlemaine and back again, it took me about 5 and a half hours, totalled around 95km.
(edit: If you're also thinking of a return trip I'll just add that I was using this as a training ride, was pushing pretty hard and only stopped in Castlemaine for water. I was fairly knackered at the end. I consider myself to be pretty fit so you might want to take that into consideration, a return trip could be a big day)
If you're starting in Hepburn Springs I would recommend starting from the end of Golden Springs Avenue – it’s easy to find the track at the end of the road, head right. If you’re ‘only’ going one direction, I think that Hepburn to Castlemaine is the most fun (more downhill).
You can buy a map from the tourist info offices in Daylesford but I don’t think you really need one.
All of the track was rideable and in good condition. A few bog holes and trees down but always a way around them. The signs are quite easy to follow, I took 2 wrong turns but it was more out of carelessness and I didn’t stray too far from the right track.
It’s a fun track especially as you get closer to Castlemaine, physically a it was harder than I expected, the climbs are short but they’re frequent and can be steep. Bring lots of water with you.
If it’s a hot day, keep an eye out for snakes.
Have fun