At the beginning there is 2 minutes, after 25% of installation there is 4 minutes. The whole installation takes about 14 minutes (at the end) in real (typical desktop installation). So there is something wrong. Anaconda used to count almost precisely.
*** Bug 81479 has been marked as a duplicate of this bug. ***
This has been an issue for many many releases. The estimate is just that. As the install goes along the estimate will be closer. There are operations going on beyond copying files to disk that make the simple projection of time incorrect.