Skimming the graphs one would say "it hardly matters" which matches the naive assumption that any advantage would be "arbitraged away" by people spending their time researching such matters.
I know it's easier said than done, but building something that people actually want will get you orders of magnitude more upvotes than whatever variance can be attributed to the time of posting.
I'm in Central Europe and prefer reading it during my morning/early-afternoon. When the east coast Americans start waking up the speed of comments starts increasing and the number of stories grows. When the west coast wakes up, forget it. Best to wait until tomorrow.
