What is a feasible way to created a time limited demo?

I have an app that I’d like to set a specific timer for people to use as a demo. I’m not sure if this is possible, though. If I save the time in a save file, the player can just delete it and relaunch the app with a new timer. Is there any sort of way that the app would be able to detect how long it’s run and close itself if it’s gone over, without using a save file?

And that said, if the person can just redownload the app anew, they could also circumvent this.

I just can’t figure out what would work. I’d like to offer some demos before putting it up on Steam, kind of get things out there before we launch our kickstarter. Can’t exactly check in with a server for this reason, either.

Any ideas?