Project 10k: time of day matters

I tend to run in the late afternoon! Just a habit I suppose. During the week it's on purpose; then I have the run to look forward to for most of the day rather than having spent all my outside time early on. In weekends that matter less! But a habit's a habit. But one day I did it before lunch. And I immediately shaved 5 minutes off my lockdown personal best! Crikey. The next time I did it before lunch I was two minutes slower than this pb again, but still, three minutes better than my best afternoon time. I am starting to assume I just run faster before lunch than after. I hadn't expected the difference to be so big! I should of course collect more data as two before lunch runs are hardly statistically significant, but I have a null hypothesis ready. 

And why would this be? Does the day wear me out so much? Do I run better on weetabix than on bread? I'm not sure! Doesn't matter an awful lot; I just want to stay fit and that PB is only a bonus. But interesting nonetheless!