If you're a natural morning person and you're at your best in the earliest hours of the day, I envy you. This is generally not when I'm most efficient or productive.
And yet, on most mornings I get up at 5:00am, and sometimes even earlier, to write.
Why? Because the advantages of dedicating a morning time slot for writing are too enormous to pass up:
1) Freedom from interruption
The phone doesn't ring. There's nothing on TV. All the normal people out there are still asleep, so no one will interrupt or distract you.
2) Positive reinforcement
Once you've finished an early morning writing session, you can pat yourself on the back and justifiably say that no matter how badly the day goes from here, at least you did your writing. (PS: this also works for exercising.)
3) More chances to write later in the day
If your morning session is an utter failure and you wrote nothing of value, you can always try again later. You still have the rest of the day. But if you have a failed writing session at the end of the day you have a failed writing day, period. Those are the days when nighttime is the cruelest of times to write.
One final point: If your morning writing session goes particularly well, you have one of the most joyous choices a writer can make. You can stop and be proud of what you've done, or you can keep going. Go for it!