How does the time limit work?
If the organiser of the event requires attendance within a specific time, the people that are invited will be notified. They will receive a specific deadline as to when they need to clarify whether they will attend or not. There will not longer be an option to attend the event when this time limit has been reached.
On the other hand, administrators can change the status of all participants after the time limit has been reached. This process is described in “How do I change others answers”?