I did complete the two 8 minute runs last Saturday, but didn't feel ready to move on to the twenty minutes of run 3. Then, the temperature dropped.
I've tried to repeat the run twice since then, but failed on both occasions.
Today it was the first 8 minute run that was the problem. I managed 4 minutes on the slightest of slight inclines before my poor asthmatic lungs cried "No more". I needed to walk for about 20 seconds, before continuing my run, up a considerably steeper incline. The 5 minute walk served me well and I was ready for the second 8 minute run. Admittedly the second run is back down the slightest of slight declines, but to make up for the 20 second unscheduled interlude I kept running past the 8 minutes and on for another 3 minutes.
The conclusion drawn from today's experience is that asthma, even slight inclines and sub-zero temperatures are not the combination for success. I usually adore this kind of weather, but I hope it's at least above freezing for my next run on Sunday