From Ta-Marbútah ة
This letter acts as (H) and (T). It sounds (H) when the world is isolate or when the word is at the end of the sentence or before a stop - generally speaking, if there is no continuation sought after the word, then it sounds as (H). If vowels are added, then (H) is changed to (T) as in this case.
And by the way, the word here should be pronounced as duktúratun (-un is called Tanwin or Nunation).