Depends on the source of the installer, and as you probably use Internet Recovery, the installer has to be downloaded, thus the long wait, as using a local installer will take less than 30 minutes for an installation.
If you want to make a bootable installation medium, you can follow these steps:
And also, my installer "progress bar" got all the way to the end, then went *back* a bit and carried on, with the "Time remaining" being reset to *minus* 20 minutes (yes, minus!)
Typical installation time using internetbre overly over a fast BB connection is 40 mins for me....as posted this will depend on your download speed as the OS has to be grabbed from the Internet and Apples servers which also run slowly at times. You can avoid this by creating a bootable ML USB stick which decrease the amount of time as the OS is on the stick.