When is Fifth World going to end and Six world to begin? *Goes to check.*
The wiki is off by... One year. 2012, December 21.
Since they are both similar, 20th and 21, and taking into account that there are different time zones, it is possible that they are correct.
In short, when one is in 21 and one is in 20, this peroid of creation will end.
And Shadowrun will begin.