Yes, it takes a VERY LONG TIME to upgrade
.... The other gotcha is -- it doesn't work very well. I tried this (I have thread here on going from FC3 to FC5) as I wanted to keep the status quo (like upgrading Windows let you) and upshot is I just wiped and installed from scratch and lost my settings
. Clean install will be much faster too.
Yes it's okay to cancel, because you are going to do a clean install from the FC5 CDs, so who cares what the 'upgrade' status is
Hopefully you have backed up the files that you want to keep.
Here is my thread on the trials and tribulations ...