Mobile pass - When I add it to the rail planner app will it automatically activate or will I have to do this myself?

I’ve just bought my mobile pass. When I add it to the rail planner app will it automatically activate or will I have to do this myself? Does the 11 month time period that I can use the pass still count once I’ve added it to the app (without activating it)? Do I have to activate it days/weeks before I plan to travel or when I’m boarding the train and will this date have to be put in when i add the pass to the app. Thanks!