In Windows, head over to this folder:
and find a file named "GameUserSettings"
Open up GameUserSettings file:
You'll see all of this text:
Scroll down until you find "SimpleMobileStats"
Under SimpleMobileStats you will see "SecondsPlayed=#######"
Copy the numbers after SecondsPlayed= and go to Google.com. Paste the numbers and type "seconds to hours":
Now you know how many hours you have spent playing Fortnite!