After the Mac reboots, try to install the macOS Catalina, Mojave, High Sierra again. Hold down the power button to power off the Mac. If you confirm that the installation is frozen, try the following methods to fix. Therefore, before taking further action, press Command + L, which will open the log file and shows you if the installation is still going on and the amount of time left. And forcing restarting a Mac during OS installation may cause data loss. So it doesn't necessarily mean that the macOS installation is frozen when the Mac stay at “20 minutes remaining” for two hours. Sometimes, it just takes a very long time for you MacBook or iMac to install the macOS Sierra or High Sierra update.
Troubleshooting macOS High Sierra Install Problems (opens new window) # 1.Check If the Install is Still Going on Calculating time remaining.' Here shows you how to confirm if the installation is still going on and how to complete the update successfully. If your macOS update also get stuck at 'Installation is in progress. The progress bar has been stuck at 40% or something, showing: 'Installation is in progress. After downloading the macOS installer, you try to install the macOS Catalina/Mojave, macOS Sierra or High Sierra but the installation get stuck. MacOS installation problem happens all the time.
