Depending on your data, your number of applications, installed, your system & hardware configuration, a Windows 7 upgrade could take anywhere from around 30 minutes to over 600 minutes.
Windows 7 Upgrade time
According to the test results that Chris Hernandez, a Microsoft Software Engineer, posted on his blog, Redmond managed to get the Windows 7 upgrade time to be faster or equal within the five percent threshold to the Vista SP1 upgrade time.
The biggest thing that stands out is the very broad range of the upgrade time: from 30 minutes to 1,220 minutes.
That second extreme is with 650GB of data, 40 applications, on mid-end hardware, and during a 32-bit upgrade.
I always suggest a clean installation over performing an upgrade installation. Better this way!