Obviously right now it is neither of those times, since I am oh-so-productively posting to HN. ;)
A regular hour office job, but largely '50% time' which I'm ridiculously lucky to have, long may it be that way.
Evenings are a time for inspiration, and mornings for licking-off stuff mainly related to admin and documentation.
Time to work with and interact with colleagues is very important. It is a magnifier. What I've learnt the most regarding my own productivity is I do too much, and it is probably easier to have others do it. That's done by sharing and influencing, and helping out when colleagues are in need.
This was true when I worked the nightshift and began working at 3pm and ate something around 5pm and was true when I moved to dayshift and started work around 8:30 or 9am and is true now when I typically start working between 9am and 10am. In all three cases, the first two hours of my day are/were spent doing relatively easy things and then more serious work happens/happened after eating lunch.
I used to come in late (midday) but commuting changes forced me to become an early riser. Now I honestly couldn't go back.