Activity Life Cycle + system.currentTimeMillis ()

Take a look here: link

Explain in more detail what I mentioned in my last comment. But basically the logic is you use System.currentTimeMillis () to save time frames that you will want to measure: when the Activity starts, when it pauses, etc.

To measure the time passed between these frames, just take the difference between them, which will be a value in milliseconds, then just convert to the unit you want (minutes, seconds, etc.).