I don't have citations, but have read data that supports the idea that exercising in the evening results in higher cortisol levels, and thus lower levels of melatonin in the evenings.
Sure, if you buy into the "you can't be a night owl and be healthy" thing (as this article seems to suggest). I think you can have both.
I feel that making people think it's somehow better to exercise only in the morning will discourage some people from exercising daily, which I feel is more important than the time of day.
The grandparent comment is also assuming that you want to sleep in the evening, which means you wouldn't be a night owl so it kind of misses the point.
There are still lots of people in this thread assuming that the "problem" that night owls face is that they're not sleeping in the evening, that's not it at all. They're sleeping in their natural cycle, it just doesn't fit with typical modern life.
So if exercising in the evening raises cortisol, and makes it hard to sleep for normal people, then that's not going to be a problem from someone sleeping at 4am.
I train anywhere from 9pm-1am and always sleep better at what seems to be my natural sleep time, which is around 3-5am.
Both your points are fine, I'm not attempting to say anything one way or the other, only to raise awareness that exercise has a hormonal response that some do not take into account.
