Deferment is not possible. In case you would get admission, you would have to finalize the enrolment process within the respective deadline, irrespective of the fact that you would not be able to arrive in Germany in time. The enrolment process is completely online.
Once you are enrolled, you can join classes any time. Late arrival is no problem; respective confirmation letters for visa issues will be provided through the application portal. In the worst case, you will lose one semester and you will commence your studies next semester. However, please note that your examination deadlines will not be interrupted by this; your obligations associated with your studies will remain unaffected.
The standard period of study for a master program is 3+2 semesters. All examinations must have been taken for the first time by the end of the 5th semester. Otherwise, they are automatically assessed as "failed" (incl. the Master's thesis). For the Master's thesis there is then one further attempt, for all other examinations you have 2 further attempts, i. e. the program is not limited to five semesters.