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They aren't sitting on the data from the main crawl for 20 days, then hit a button and it suddenly starts the update. If that were the case it would almost certainly happen during regular business hours, pacific time.
He might have a better guess than the rest of us, but the dance starts when the prior steps are complete.
While there definitely is some processing of that data gathered from the month before by the time the dance starts, it does seem that the most of the crunching of it goes on during the dance. This is why we have a dance where things are in flux. Otherwise they could just throw a switch, and that would be the final update. One thing I've noticed is that it seems that PR doesn't get fully factored in until the end of the dance. For example, on some dances I've ended up early at #1 for an important keyword search, over other sites with higher PR than me. But by the end of the dance I end up #5 or so on that keyword. It is also quite possible that inbound link text isn't fully factored in at the beginning of the dance. The early dance seems more based upon on the page factors.
Some study came out earlier this year about this. Apparently as the pigeon's body moves forward when it steps, the head moves back at the same rate, effectively keeping it still for a moment, at which time it takes sort of a still snapshot of it's surroundings. Maybe that's what the update is - a pigeon head bob.
How true...now, if you can write an effective subSCRIPTion, you can probably retire (assuming you're not already...)
More than 500 carefully screened Researchers are ready to answer your question for as little as $2.50 -- usually within 24 hours. Your satisfaction is completely guaranteed
How about asking when the update will happen [answers.google.com ]
Best regards as always...
CS