Another double

Having bailed on my Tuesday run, due to needing to get to work early and being super tired at the end of the day, I decided today would be another double. The plan was to do the easy 4.5 miles in the morning and the speed session of 8x400m. In the evening.

In the morning I was so cozy in bed that I refused to get up for a long time, but eventually I did. I almost didn't run, but decided something was better than nothing, so I went out and did 2.5 miles easy, the first mile and a half were hard. These recovery runs are important to loosen the muscles. I really wish I could just do them at lunchtimes sometimes. Any way, paces:

Mile 1: 10:03
Mile 2: 10:12
Mile 2.5: 9:22

I left work a tad early to get the evening one in. It was really warm and humid on the train and by the time I got into Colchester I was really tired again. I was considering bailing on this run, as I had so much else to do this evening, but I felt bad given i had given myself an extra half hour by leaving work a bit early. After arriving home I decided I would get into my running kit, and it worked, after I got dressed I sat down for about 2 minutes before deciding I wanted to run. I programmed it into the garmin. The session was 8x400m, and I set the rest interval as 90s. I think next time I can certainly reduce this. But, after I looked at the session I was super impressed with my speed. I'm not sure what speed I should be doing 400m reps, but here are the paces:

Interval 1: 6:48
Interval 2: 6:24
Interval 3: 6:27
Interval 4: 6:46
Interval 5: 6:09
Interval 6: 6:55
Interval 7: 6:32
Interval 8: 6:35

The fact they are all under 7mm impresses me, but I really don't know if these are good paces toward an 8:20 paced half marathon, which is why I don't understand why this session is part of a half marathon training plan, but hopefully it'll help my 10k!