Hi Claire
I'm not sure how long it takes, I never got there!
We set off walking one July morning and had to turn back halfway up the hill - it was far too hot to carry on. So, when you do it in August please be careful. We had lots of water, the right type of shoes, a hat and everything, and still had to turn back. We are both regular walkers (today we're doing a 7 or 8 mile walk around the hills of Holmfirth) and decently fit but it's not 30* in Huddersfield today
The village itself is well worth the trip - we went up in a car, had lunch at a restaurant, a few beers, and the view towards Agios Georgios is a real jaw dropper. And jumped in the pool 10 minutes after leaving Afionas.
If you do the walk it might be better first thing or later in the day.