Assuming everything goes well and nobody destroys the altar:
If I recall correctly, destruction was commenced last Thursday morning (Europe time), which means the world will be destroyed the morning of February 18th.
After the world is destroyed, will the new one start immediately? I assume there will be some hours in-between for map generation and other setup, but is it reasonable to assume it will be playable starting late Thursday afternoon?
I'm strongly considering taking that Thursday and/or Friday off work to play the new world, so it would be nice to know when it starts.