I'm fairly certain it varies greatly for everyone on a day to day basis. Estimating hours played is too difficult to do.
Some days I play nothing, sometimes for a week I don't play anything, then I get the urge to paly, and play like 4 hours a day for a couple days straight.
Other times I play pretty consitently around the same time everday (I play picross in bed before sleeping).
It all depends, but all I know is I get tons of use out of the thing, and I am so glad that I bought it.