ofcourse you can take any later train aswell :) just add these trains to your pass :)
Because you can“t delete a already activated travelday on the day itself i recommend to add trips only last minute to your pass that way your are full flexible and can even decide to stay 2 or 3 days longer at a destination :)
Here for INland=domestic travel in NL-all main routes have trains at least ev 30 mins-and in the main city-area much more often. There are NO REServations nor even possible. Its another thing for some trains to Germany or Thalys southwards.
Its more like a grand scale metro-including the cumbersome gates.