The question has occurred to me on occasion.  My answers will be less than satisfying, to be sure.

• In the morning.  The morning always seems like a good time to write.  The mind is fresh.  Brand new perspective and all.  Problem is that I rarely rise early enough to get a little quality time in for myself.  I have thought of things on the way to work, though.  I’ve written them into my iPhone on the parking shuttle.  Some of them turned out not half bad.
• While drunk.  I think it was Hemingway who said, “Write drunk. Edit sober.”  I’ve written some decent stuff while buzzed.  I even still liked it when I sobered up – though it did need some sober editing, sheesh.
• While writing.  There is a school of thought that says anytime the muse visits is a good time to write.  In my case, the muse seems to visit typically only while I’m writing.  Another way to express this idea is that I never trust anything I think about writing unless and until I am actually writing.  Many a good idea has stunk up the page once put down on paper (or pixels).
• After warming up.  This is similar to “while writing”.  I wrote more than a few of the 90 in 90 posts that I am proud of only after I forced myself to put my fingers on a keyboard.  I was in no mood.  But once I started typing, the muse showed up.  So, warming up by just writing anything (like journaling or copying something or messing around) can sometimes turn a bad time to write into a beautiful time to write.

Hey.  It turns out that right after dinner on a Wednesday is an okay time to write.  Did I answer your question?