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 :)