'''A couple millions years.'''
It can form in seconds.
Unknown, but one theory is appx 240m years. There is much that is still not understood about the mysterious geode.
Uranium forms almost instantaneously in supernova explosions.
It typically takes 30-45 minutes between when a thunderstorm first starts roatating and when it produces a tornado. Once a tornado starts to develop in can touch down withing a few seconds.