Time to the high point - 12 minutes jogging all the way (although I needed a break when I got there).
Time to Machen bridge - 24 minutes.
I jogged up from the main road to the cycle track and kept going all the way along the cycle track, back down to the main road, along and back to Waterloo (53 minutes) and the jogged back up to the high point which took an additional 14 minutes.
I definitely needed a break after all that so I had some more of my energy drink and watched the sun set behind a hill across the valley. After resting a bit I walked / jogged back into Waterloo and got back 33 minutes after I started the second circuit. I'm quite pleased with this and my legs don't feel too bad right now, although the real test for them will be the next two days sitting around at work.
Right, off for a shower - got to wash the sweat away :)