pas

You can activate it at any time, but that is not recommended in advance. It's a good idea though to do step 1 and 2 of the reservation procedure in advance. You could also test the activation (step 3), but be sure to select a start date in the future because you can't cancel activation once the validity period has started. That's also the reason why activating in advance is not a good idea: if anything happens after midnight of the day you start your trip (e.g. you wake up ill), it will be too late to cancel. Also, I've seen multiple stories of people who activated their passes, then postponed their trips and forgot to change the start date, only to find the pass had expired at their rescheduled start date.

You will be able to add a journey to your pass after activating the pass. Activating the first journey of the day activates a travel day and generates the ticket for that day. Here again, you should not do that in advance.