If students move up from the waiting list and are regularly registered until 48 hours before the exam, they receive their access-authorization by email. Students, who move up within 48 hours before the exam, can access the confirmation in their "Favorites" in TISS. This is also possible at short notice in front of the TU Wien building.
However, it is not possible to take the exam without an access-authorization. Therefore, students who are on the waiting list before the exam date and have no access-authorization at least 30 minutes before the start of the exam, cannot take the exam.
You can find more information on presence-exams in the Guideline for Presence Exams at TU Wien.