RhinoFish - 4:05 pm on Mar 25, 2013 (gmt 0)
At the bottom of the interface page, it says:
Reporting is not real-time. Clicks and impressions received in the last three hours may not be included here.
The data I see tells me that's pretty accurate, after 3 hours, usually good. It's most often faster than that. Segment by hour of day, and you'll see it piling up.