From a Primal standpoint, both options are valid. Deer, for example, feed, primarily, in the pre-dawn and pre-dusk hours. That's why hunters, typically, get up so early. So Grok would have his most successful chance of catching one either the time right when he wakes up (or even before) or near the end of the day (right before dinner!).
From a modern standpoint, it's really all about personal preference. I prefer to work out closer to the end of the day b/c I get up really early for work and generally just hate mornings
Some people like to start their day w/ a workout b/c they either feel they won't do it if they put it off until the end of the day or b/c it makes them feel energized for the day ahead.
If I were you, I'd mix it up depending on how I felt. If I felt good in the morning, then I'd workout b/c if I end up having a bad day at work, I might want to just skip the workout. On the other hand, if you're not feeling your best in morning, then give the day a shot and see how you feel in the evening and try knocking it out then.
Probably, the more random you keep it, the more Primal you'd be anyway!