Q. How can I find the installation time of my Windows 10 system?
A. Each time you deploy a new branch it updates the installation time you would normally find via InstallDate. To find the original installation date of the OS you can instead look at HKEY_LOCAL_MACHINE\SYSTEM\Setup. There will be keys for each installation named Source OS (Updated on <date>). If you go inside the key there is a value InstallDate. This is the UNIX time (number of seconds since 1/1/1970). To convert take the decimal value and use in a UNIX time conversion tool, such as http://www.onlineconversion.com/unix_time.htm. This will show the installation time of the OS. Therefore find the oldest value which is the original installation time of the OS before any later branch deployments.