How often are the status of keywords updated?

Just wondering how often keyword performance is reviewed by Google

[kilo]

I was wondering if anyone new how often the status of keywords (as displayed on the accounts page) is updated? I read that it is automatically updated after 1000 impressions to the entire account. So does that mean if my entire account obtains an average of 7,400 impressions from all its keywords together, then my account gets reviewed 7 times a day by google?

[cgrantski]

I'm not sure that's the correct rule. Mine changes after far fewer than 1000 during a day. It seems more like a time rule (x minutes or hours).