Don't ask how long it will take to finish
Mountain Lion is to software commentary as certain politicians are to comedians: they both provide a whole bunch of new material.
Here's something lovely I encountered the other day while installing. After watching it count down from "20 minutes estimated", I was rewarded with this:
Yep, apparently Cupertino has tamed the mighty tachyon and has started using them to create time-traveling installers.
Of course, two minutes later, it flipped to this:
All said and done, it took about an hour to finish. No Deloreans were involved.