>Are stackoverflow pages ( such as Questions, main pages of a posted question, profile page) auto-update?

Yes. Not exact auto update but it will give you notification at the top of the questions list. Like this:

>![enter image description here][1]


>If so, what is the update interval?

When new question is added or a question is updated.

  [1]: http://i.stack.imgur.com/I7qOT.png