Hi, I can help you out , I have 4 years of experience in developing android apps. you can see my portfolio.
and Now about the app, basically you need an app in which you can select a file,app, or web page to open after a specific time or after using specific app for specific time.
I have a question here, which kind of File do you want to open. e.g If it is a web page so where you want to open it , in your app or chrome browser.