Your looking for a way to determine how much time has passed since the person last played your game?
HaxO gave good advice here, as all would need to do is store the time in a save file when the person exits the app. When they start the game again you calculate the difference between the current time and the time in the save file and that is how much time has passed. There are blueprint nodes for doing this.
Is there a game or a mechanic you have in mind when talking about Android? Give us an example of what you want to achieve and we could possibly figure out how they accomplish it, remember though when you close the app, there is no longer a process scheduled to execute on the CPU, doesn’t matter whether it is Windows, Mac OS X or Android. Unless a true simulation, most games use trickery to achieve the desired effect.