The length of the RT Practical is dictated by the candidate who controls the speed at which the test progresses. The two extremes being that it must not take any longer than the flight plan time for the given route, and must be long enough for the candidate to make all necessary calls.
The examiner has no control over the time, as he has to wait and follow the candidate. 30 - 45 minutes is typical.
You are not allowed to take anything into the test; blank paper and a pen/pencil are provided.