Don't remember it taking that long once the update had downloaded and installed. Give it another 10 minutes maybe, then try backing out if you can (I think the Options button will allow you to), and then trying the update through Settings > System Update again (see
here).
If there's no backing out, you'll probably have to reset it. If you have troubles restarting, you can go into Safe Mode (instructions here) and then either run through System Update through there, or Initialise it to get back to default. Worst case, you might have to download the latest copy of the software and use the Reinstall System Software option - let us know if you get there as I did this when I installed upgraded HDD so can run you through it.
Hope you get it sorted - if you do, very much recommend Resogun - still free through PS Plus subscription and one of the best games out there.