We did it on a lovely sunny day in January last year and, like everybody else has said, it was definitely worth it for the views. I can't remember how long it took us, but it was less than an hour I think, and neither of us were particularly fit at that time (I'm still not, but Mrs kcdc230 is on a complete fitness regime at the moment).
Even at that time of year the cafe was open - we were the only people at the top when we got there, but the cafe was still open and we had a couple of drinks as I recall. I'm pretty sure it had food for sale as well.
And look out for the cats as well. Not sure how active they will be in the warmer weather, but we were amazed at how many there were - I've got a cracking video on my phone of about 20 of them emerging from a tiny hole in the side of a brick wall!