The best time for me to write is early in the morning. Right after I've woken up, brushed my teeth and taken care of morning basics. Then I hop to the computer and let it flow out. It just seems like I am more creative and writing is easier at that time of day. Perhaps it's because I've been dreaming all night and occasionally I get some of my writing ideas from my dreams. I can also write better on days that I have the day off from work and can relax some.
Unfortunately, I don't have the chance to ever do this except on Saturday mornings which is why my creative writing gets a lot less attention that the freelance articles I do. I can write them anytime because it's basically just stating facts and research to help someone make an informed decision. After a day at work, I find that my creativity is completely gone. I am empty of anything good and happy. I definitely understand why they call it the daily grind. Because it wears you down in every way - physically, mentally, emotionally, spiritually.