There is none- IF a new to be made trip has added on a day that has by then not yet been activated, then it wil simply start as a new day and you get 13/15 etc. The QR code will work for the whole day, but still every new trip on train has to be added.

AgaiN: be wise, there are sooooooo many reports here about people adding days and forgetting to delete when they found the trip could not be made or plans change-do it really ALAP= as LATE as poss

A travel day is a 24-hour period that lasts from midnight to midnight. Within this travel day you can take as many trains as you wish. A journey, however, refers to a single train taken on a travel day. For example, if you added the route Amsterdam → Paris on September 20th departing at 10:00 that would be a single journey. However, the entirety of September 20th would be considered a travel day. After arrival in Paris, you could take another train to Lille, it would still be the same travel day (September 20), but it would be a different journey. You can read more about how to set up and use a pass on this page. 

You can cancel a planned travel day up until 23:59 before the day is due to start. Unfortunately a travel day cannot be cancelled or undone after it has already started.