Most "mobile app" ideas can be validated fairly easily, with a few weekends' worth of time at most. Put your MVP out there. Spend a few more weekends fixing problems and responding to user behavior. If it doesn't generate any revenue, throw it away. Try something new. Rinse and repeat. If you finally stumble on something that sticks, then you can allow yourself to focus on it full-time.
Most "mobile app" ideas can be validated fairly easily, with a few weekends' worth of time at most. Put your MVP out there. Spend a few more weekends fixing problems and responding to user behavior. If it doesn't generate any revenue, throw it away. Try something new. Rinse and repeat. If you finally stumble on something that sticks, then you can allow yourself to focus on it full-time.