"Windows PE is not a general-purpose operating system. It may not be used for any purpose other than deployment and recovery. It should not be used as a thin client or an embedded operating system. There are other Microsoft products, such as Windows Embedded CE, which may be used for these purposes.
To prevent its use as a production operating system, Windows PE automatically stops running the shell and restarts after 72 hours of continuous use. This period is not configurable."
Source: https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/winpe-intro
Windows PE does not include any Windows license keys. Additionally, Hiren’s BootCD PE does not violate the purposes of Windows PE and it does not alter the "72 hours of continuous use" limitation. Therefore, using Windows PE in Hiren’s BootCD PE is legal according to Microsoft’s usage terms, in our opinion.