How to save start date timestamp of free trial of my offline Windows App?

  appdata, licensing, security, trialware, windows

I wish to distribute a Windows App with free trial. The app can run in offline mode, so I need a way to verify free trial expiration.

For that, I need to somewhere save in Windows the start date of free trial. How should I do that ?

One way I thought is to encrypt the timestamp with a password (known only by my app), and then save the encrypted data as .txt file in AppData/Roaming directory.

Is this method secure enough or does Windows provide an official way to save this type of data ?

Also, if the user changes system time before free trial expiration, then my method will fail. What is the solution to this ?

Source: Windows Questions