A binding and valid exam registration (regardless of any additional selection procedures at the examining chair) always have to be done within the published registration period via FlexNow.
If there is no registration in FlexNow, there is also no examination entitlement and no performance can be credited.
The registration and deregistration deadlines for the exams (separately for Bachelor's and Master's exams) as well as the exam dates are published on the homepage of the examination office from the beginning of the semester. Changes and updates are also announced on this page.