So I did it today. I don't think I've ever been so sweaty in my life as I was when I finished it, and I was a shade of purple seldom seen in nature, but I did it!!! I can run for 20 minutes!!
I felt utterly knackered through most of it, but the last 5 minutes was the easiest. Then afterwards I got a huge buzz and didn't even need a sit down to recover.