No-one knows - I'd be interested to see the stats for the most popular reading times for the world as a whole.
I work by the 'Breakfast in America' theory - I'm aiming my comic at America and Europe (though of course everyone is welcome to read it) so I post at 4am PST - which means it's ready for everyone to read over their cornflakes on both coasts of North America. In the UK, where I'm based, it comes out at midday, and most of Western Europe sees it at 1pm - so that's the lunch break covered as well.
But our audience is worldwide, so I'm not sure there is such a thing as a right time.