DD1 is 4, DD2 is 2. It varies. Probably on average they'd watch 4-ish hours / day, mostly ABC2, sometimes recorded shows (like for when Nat says, "Mummy, it's STUPID Grandpa in my Pocket! NO ONE likes that show. Please can I have something different?)
I have it on while I do morning chores (putting out washing, cleaning up breakfast) and in the afternoon/evening when I'm bringing in washing/cooking dinner etc. Also just before bed they will watch Giggle & Hoot. We are usually out and about during the middle of the day.
Having said all that, TV doesn't do a lot for DD2 who generally plays with other toys or reads books while DD1 is watching. Unless it's playschool, Dora, Peppa Pig or a Justine Clarke DVD - those she enjoys. (Though I have seriously limited the Dora viewing recently. That chick annoys me.)