I had a website get hit on 5/31. It was ranking very well, all the way up to 5/30 and the next day, it tanked. I figured I got caught in one of Google's update. Like most, I decided to wait it out. As of today, I still don't rank for any keywords. Now, I am trying to determine whether it was hit, by Panda or Penguin. I did some research on Google's update release dates. There was Penguin 1.1 on 5/25 and Panda 3.7 on 6/8. I have always assumed it was Penguin, because I have 900+ backlinks and 875+ are targeting the same keywords. My question is, when Google releases an update, does it take effect immediately, or does it take a few days?