W6R3 done!
It was hard, mainly because it was so cold and the wind was cutting.
And I managed to get confused about the timings. On the app I use, the 'narrator' tells you when each 5 minutes has passed. In my head I'd already done 20 minutes and was waiting for her to say the final 'well done, just a minute to go!' - but actually I still had another 5 minutes to go 
Then at the last minute, I ran past a little girl, probably about 3 years old, who looked at me, smiled, and then started running with me. That really made me pick up my pace - I wasn't going to be beaten by a small child 
Feel good about the achievement, but I can definitely tell I've been doing some hard/heavy breathing, and that my lungs have had a good work out. Knees feel fine so far
Start week 7 on Saturday.