How to make an App that only works for a week?

I’m developing an Android app focused on business marketing and one company has asked me to send via email the APK file to evaluate if they will use the app.

But to be honest, I’m afraid of them steal my app. So what would make me safer would be to create a version of my app that only works for a week, and then just stop working. Is it possible to do that?

An easy way, but also easy for them to bypass if they want to do some research, would be to use playerprefs to save the date that the app first ran, then in subsequent runs, read that variable, and if the date is over a week ago, pop up something telling them their trial is over, and exit the game when they click on an ok button, or whatever on that trial over window.

A little more secure would be to communicate with an external server, disable the app if it cant communicate with the server, and store their initial run date on the server. I would also get the current date from the server as well, so they don’t bypass this by changing the date on their device.