Each of my downloads took less than 10 min each. I needed to Root by Tablet before installing any of the JB updates so I kept stopping the download by rebooting during the download. But after the reboot the download would simply pick up where it left off. So I let it finish downloading. I was surprised to see that it didn't automatically install on it's own. That allowed me to finish the Root process. I backed up my Root, verified that it was saved, then I installed the upgrade. In the following weeks there were two more upgrades, both installed without any problems. If you haven't tried rebooting your Tablet in hopes that the download will restart you may be able to delete the update that is stalled by using your File Manager, go to the Root Dir and trying to delete it there.
If that doesn't work, as a last resort you can always reset your Tablet in the Settings, Backup, Reset to Factory defaults. This will erase all of your Apps and settings that you have accumulated thus far, so if you want to preserve it then backup your apps that were downloaded from the app store using ASUS App Backup or something similar. Don't backup any system apps because they will be updated during the OS upgrade. Then do the Factory reset. Once done, the OTA update will start downloading again. Once it finishes downloading and you install the update, then you can restore your App backup. Good Luck.