I've switched from tracking hours to just tracking containers more accurately.
Today wasn't a great day for drops. In 100 runs of 21 containers, meaning 2,100 containers opened, I only got 1 blue crafting recipe.
if your 21 containers are like my 21 containers than it is actually 15-18 containers, since there are usually at least 3 empty.
also, i have noticed that the wayrest bank, for example, where my '21' container spot is, is actually only 19 since 2 desks are always empty. add in 3 random empties and it is actually 16, although i think the actual average number is between 14 and 15.
i do agree with the premise: hours played is largely irrelevant since there can be a huge sway in the rate of containers opened. containers opened is a direct, and i would expect a much stronger correlation to drop rate.
i have seemed to get a better drop rate in off-peak playtimes. i know some games have throttles to slow drop rates if many people are looting a particular item. that may be in play here, or it may well just be the RNG at work.