I had begun on the second running stretch, and when I passed the 200m point, I thought: "Well, I still feel fine, let's see if I can do 400m!" And then I ran on to the 600m. And then I felt adventurous, and went for the 800m. And lo and behold, I was still not too tired, so today I ran my first continuous 1000m.
After that I did a walking stretch -- not because I had to, but because I didn't want to overexert myself. I'm sure tomorrow I'll pay the price in terms of muscle- and shin-aches, but tonight I'm feeling good about myself!