In a Google hangout yesterday with Google's John Mueller, John explained 31 minutes and 47 seconds into the video that Google updates their data for manual actions within Google Webmaster Tools twice a day on average and then only sends out emails once a day on average with notices.
He said:
I believe webmaster tools data for manual actions updates, maybe, twice a day. Something around that range. And emails we may send out once a day.
He said this in regards to why you may get an email notification of a manual action but when you check, there is no manual action. There can be other reasons, such as manual actions expiring. But all of this is rare and it isn't common to see this happen often.
Here is the video:
Forum discussion at Google+.
