How to signal that a Use Case is over?

Let's say I am making a Use Case about filling a quiz. You have only 5 minutes to fill that quiz. When doing the Use Case for "Filling the Quiz", how should I signal there is a time limit and that after that the Use Case is finished? I simply write it by text or is there anything more formal to use?

Sketch of what my Use Case can be:

 1. The Actor tells the System he's ready to start the quiz.
 2. The System presents the Actor with the first question of the Quiz and its 4 possible answers and tells him how much time he has left.
 3. The Actor tells the System what is his chosen answer (a number between 1 and 4).

Repeat steps 2-3 until there are no questions left.

 4. The System registers the results of the quiz.

I could just put operations between 开发者_运维百科all those shown above to check whenever the time left is over, but there is probably a better way to show this.

Thanks

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You can use an alternative flow timeout case, like

Alternative Flow 1: Timeout
2. The System detects that ... 

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To be a bit more precise, but agree with the other answer in general, for this situations Alistair Cockburn (Writing effective Use Cases) recommends using extending use cases (alternate flows), which would have in their extension points the time limit. In textual form, you can easily use the range of numbers of lines of scenario lines, where the timeout can happen.