The absolute best time to ever post, hands-down is midnight PST.
That's the point that google starts counting the day. You want your video to have a full day to marinate and do whatever it's going to do and you give it a fighting chance in the search engines if it's up there for an entire day. People make the mistake of posting later and it messes them up in the search.
Example: If I posted a video at 11:32pm and it only got 5 views? YouTube will look at that video as only able to attain 5views in a day, not the fact that it's only been 30 minutes even though the time may say "posted 1 hour ago" on your end? To the world and the spiders it says "posted on 29th of july"
Social media marketing? that's another story. Example, if you want to market on twitter to your audience of teens? You would want to post around the time they are most likely to read it... like when they get out of school etc.
but YouTube? Midnight, guaranteed!