I am accessing the app from home. You just have to log in before park opening and the “My Status” and “Join Boarding Group” buttons will be active for you during the brief window when BGs are available. It will just kick you out at the step where you haven’t entered the park yet.
Yes, the consensus is to press “My Status” and it will refresh from the server and allow you to click “Join Boarding Group” faster than just staying on the “Find Out More” screen. Read this post for detailed instructions with screenshots.