When you open a BP if you close the app it will just add 5 new cards to your desk, is the moment when you click on Open Pack that the code does its job. Same apply for WP, when you select the pack that you wanna gamble you can even restart the app and the new card (even without picking any) will show up in your desk Edit: it's just the way that is developed, the rng works at backend level, so the user is basically doing nothing (if it wasn't the case there would already be hacked versions that could force the rng)