How can I run an Android App in Foreground automatically?

Well, I'm developing an Android App, and I need to know if is possible, and if so, how can I do the App behave that way:

The app would be running in background, and after some kind of trigger, such as time, for instance, the app would back to run in foreground, or pop in the screen.

You run the app, just as usual, and after you exit it, it runs in background. That's what normally hapens on Android devices, when you dont close the app properly. I wanna know if its possible to call the app back without select it, for example, at a pre-defined time, like 8 o'clock, the app would go back to run in foreground.

If you know some function that minimize the app, an maximize, that would suit, I guess.

I know i can use the System.DateTime to get the device clock, but I don't know how to call the app back.

If anybody can enlighten me on that matter, that would be fanastic.

Thanks;