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I'm not an early morning person. I need to get in that first meal and give it some time to digest before I do any strenuous exercise. But, everyone is different.
I'd say run it at a similar time to when you run normally. If you usually run first thing in the morning, then you should do the PRT in the morning. If you're an afternoon runner, then do it later. It's all about when your body is used to running.