This is one of the reasons why you will often see software installation look linear [10min until it is finalized, 8min until is finalized...] even though on a micro-scale, the process may be oscillating a lot more.
If the progress bar doesn't differentiate which stage it's in then it's purpose is mostly just to let the user know it's doing something.
That has always stood out as one of the more impressive engineering feats I've seen.