I've just run 5K to test out what I can do. I did 22:52. The course is far from ideal, I have to run up and down on hills and bridges, and I have to cross a busy road once in both directions, which I do by running on the sidewalk, and glancing back over my shoulder if there are no cars and I can cross.

This makes me a bit optimistic. As I wrote before, my minimum goal is 24:00, and now I proved it for myself that I can do it. In fact it is probably going to be fairly easy, unless I seriously screw up something. I will start to pace myself with a 23:00 goal time, and I will try to speed up at 2 miles, if I'll have any reserve left. I might get close to 22 minutes if everything goes perfectly.