I don't know when this will occur. I expect that will depend on the Earth and the overall plan as it is her ascension and evolution. Many people feel it will be in this life time - especially with reference to the fact that various older calendars end in 2012.
I don't really think about the 'when'. I don't think it matters at all. I believe the ideal space to be in would be one in which we are content and fufilled in each moment and not wishing to be elsewhere. I think for those who are longing for this to happen, it's perhaps an idea to check if there is something for them to release - long term weariness perhaps.