Some good information here:
Resetting Windows Activation
When you install Windows with a single license product key, you have 30 days during which you must activate that installation of Windows.
There is no limit to the number of times that the Sysprep command can run on a computer. However, the clock for Windows Product Activation begins its countdown the first time Windows starts. You can use the sysprep /generalize command to reset Windows Product Activation a maximum of three times. After the third time that you run the sysprep /generalize command, the clock can no longer be reset.
When you run the sysprep /generalize command, the activation clock will automatically reset. You can bypass resetting the activation clock by using the
SkipRearmsetting in the Microsoft-Windows-Security-SPP component. This enables you to run the Sysprep command multiple times without resetting the activation clock. For more information about this setting, see the Unattended Windows Setup Reference (Unattend.chm).