How to check OS install dates for quarantined statuses.
Hold down the Windows Key and Press R on your keyboard.
Type in cmd and Press CTRL + SHIFT + ENTER.
Type in systeminfo and Press ENTER.
Open the console window in the Utilities folder, as outlined above.
Navigate to /var/log, then click on install.log
Scroll all the way to the top of the list, until you see a series of text that says "OSInstaller"
The date next to the text is the install date.
Open the console application found in Applications > Utilities > Console
In the sidebar select "Log Reports"
In the top half of the window select "install.log"
The lower half of the log window scroll up to the earliest possible date to see the install date.