Not necessarily. Schools can choose to start the examination at the Key Time if that is convenient for you. Or you can choose to start the examination before the Key Time if that is more convenient. But if candidates finish before the Key Time then you must arrange for the candidates to be kept under Full Centre Supervision until the Key Time. A few schools may wish to start the examination after the Key Time. This is also fine, however, the candidates must all be present at the Key Time and you must keep them under Full Centre Supervision from the Key Time until the start of the examination.
Our interactive tutorial here explains some of the main regulations for timetabling examinations and will assist examinations officers in implementing them in their school.