Should only take a minute or two. You're the second person that reported this, but I (and all the testers) never ran into this. I'll enable a debug/verbose mode so you can see what's going on. I have it set to hide all of it cause it scrolls a ton of useless information.So it should not take 20mins, but how long should it take? I have been stuck at "preforming pre-update" for about 10mins now.
For now, try killing the program and restart it. Also, try right-clicking and running as Admin.