The best time to post is the time nobody knows about, thus posting a time in here will render any "best time" suddenly moot, because all of a sudden everyone knows about it.
But, actually, the formula has changed a lot since the new trending mechanics came into play. It used to be that, assuming you have a following base of "readers" who have you on their list and read every new chapter you post, posting as soon after 24:00 GMT (server-time midnight) as possible would at least get you powerful enough engagement from your readers to move you up on trending.
Now, however, assuming you have a good chance of making it to trending, your best bet is actually 6-12 hours BEFORE server midnight, that is because now it tracks engagements such as chapter comments. People who read in the first few hours don't tend to have quite as heavy engagement, it's only a few hours later that the discussion thread starts really heating up, and a lot of them actually like to READ just after server mid-night anyway for some odd reason. (Maybe the readers know the mechanics and are trying to game the system in their favorite author's favor.) I get my largest amount of engagement right after server mid-night no matter what time I post my stories.
Overall though, if you don't care about the trending list or don't feel you have a chance of ranking on it, anytime is fine.