There has been a train of thought I heard many years ago, that the best time is about 2-4PM, as the body is most alert, supposedly roughly between most peoples getting up and going to bed times, though obviously, peoples sleep pattens / work patterns might affect such a statistic, as obviously a night worker isn't going to have peak alertness at 4PM, if he gets up at 3PM .
That's not a problem. Like I said it's just a train of thought that's been around for some time. I don't think if someone gets up and works out, compared to doing it 7 hours later, is really going to derive significantly less benefit if at all.