What is the expected timing of tracker updates?

I know that if a torrent isn't private and is stalled for two minutes there will be one. And you can do one manually as frequently as once per minute.

Outside of these situations, how often should one be done?

The bittorrent standard is 30 minutes, but i've seen it 60 minutes too.(?)
I think George or Ivan can give you a better awnser.

Yeah, I was wondering if there was a situation in which it should be less than 30 minutes. I've been seeing it update roughly every 3:45. I think it only happens if a manual announce has been done and / or there were no new peers between announces, but that could just be the torrents I happen to be on the last two days. I wanted to know if this was intended; if not I'll look more closely at what's happening.

Tracker specifies announce interval and KT needs to obey it.
Exceptions are manual updates and "stalled for too long" updates which are only enabled for public torrents.