When are sites shuffled around in Google?

Hi everyone,

I'm wondering if Google has a set day/time or schedule where it re-analyzes rankings and shuffles sites around accordingly...or is this action taken on a randomized basis?

Thanks

 

im pretty sure its all random

 

maybe Google has the schedule for update PR, but never inform us.

 

Of course, Google does have its routine in updating PR. I think it might be 2 to 3 months.

 

its a giant program that is handle all these things................................................they are not doing this mannually..............