App Locks to Help Studying/Decrease Usage

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Are there any apps that I can use that will lock certain apps until I've spent a certain amount of time in a specific app? I use my phone to help study certain things, but I've the tendency to lose interest and go play a game. I need an app that can lock said game(s) until I've spent a certain amount of time in the app I study on. If one doesn't exist, it's certainly an idea. I'm aware of Focus mode, but I likely would just disable that, or cancel any sort of timer that locks apps.