Everybody has about the same budget, and depending on the site, that's when the labor force is at work maybe? For something tech like Gizmodo, the posting pattern might correlate to a workday based on a certain region. Buzzfeed would have a staff that goes 24/7, maybe spread out globally or just with a labor pool with some people willing to work the Graveyard Shift from home. Some content probably has to be "timely" whereas other pieces can be on a production schedule so to speak. Just thinking out loud here.