I'm not necessarily disagreeing but what makes you say working extremely early hours is probably healthier than working extremely late hours?

I wake up at 4 most mornings. I'm always at the peak of my energy at the 3.5 hours I have before I walk entirely uphill to work. After my descent I'm usually too worn out to get anything productive done, and since I start wrapping up my evening around 7-8, I don't sacrifice sleep.

My Chinese teacher put it best: "Early to rise, early to bed, leaves you healthy, wealthy, and socially dead."

Nice to know someone else is waking up really early. I started setting my alarm 5 minutes back each day toward my goal of waking up at 4am. I started at 7am now I am at 4:40am and I'm really liking it so far; I get stuff done this way.

It depends on your situation but I find that it's easier to focus at the beginning of the day after a good night's rest than at the end of the day when your mind and body can be tired.

I also tend to (for various reasons) get better quality sleep if I go to bed early and wake up early. Human sleep cycles have probably aligned with the sun for a long time which (might) have biological effects favouring this type of circadian rhythm.

Plus seeing/photographing magnificent sunrises feels good :)