Probably an hour or so daily. It is the only website that I visit daily as well. Mostly commuting to and from work, as well as during my lunchbreak.
In the weekend usually when I have some time that I wait for something. Like waiting in line at the shops - so probably less than an hour during the weekend.
Maybe an hour or two on the site itself, but it usually spawns off a couple more hours of reading/research etc.
Too much and not enough? It's little bits distributed across a lot of time. Always thoughtful moments great engagement and a simple ui. I could wish for markdown and more improvements for tablet reading but it would probably die in a rewrite. Better left alone.
I feel in awe of the people who post original content.