Have you ever sat for an hour while your computer displays 5 minutes left? It is very common for the progress indicator on the computer give you a totally inaccurate reading. You may wonder why it is so hard to make an accurate progress indicator.
The reason that progress indicators are largely useless is they often do not have a good measure of the amount of time the steps will take. Imagine you were trying to calculate how long a road trip would take by counting the number of roads you would travel. All trips using 10 roads are not created equal. You could have a ten minute trip or a ten hour trip. After you have completed your trip on five of the roads you are not half done.
These same issues hold true for progress indicators. You may be processing 10 files, but one of the files may be larger than all the other files combined. If the large file is the last file you will quickly process the first nine files, it will take longer to process the last file than it did to process all the previous files. So the progress might show you are almost finished, even though it is less than half finished. 
To be accurate, progress indicators have to measure something that will closely match the amount of time the task will take. If you are a measuring the time it will take to travel between two places, miles is usually a good measurement unless there is traffic or an accident. Hopefully progress indicators will improve, but until then take what the progress indicator is telling you with a grain of salt.
It is generally a good rule of thumb to try to do upgrades or installs when you don’t need the computer for a while. When you have finished for the night set off that software upgrade and it should be done by morning.