Tired, hungry or traumatized (you know, that - I didn't get a turn - kind of trauma), it can go from 2 seconds to 2 hrs. Well, it's never been two hours, but it's been an hour! My ds doesn't say a lot during, his vocab is huge, but he can't always use the words very well - grammer sucks - so he just fights us, cries, wants to be by himself sometimes. Pretty much anything goes, though - occasionally (recently) he'll say mean things to his sister, who is 6 yrs older than he is, so she can push his buttons pretty hard. Mostly he is fine if he's fed and not tired, though.
It's SUCH an amazing age!