As Bend and Zatota indicated, you will have to let the prosecutor know whether you are pleading guilty or going to trial. If you are pleading guilty, they will call your matter up before the trials. If you say you want to go to trial, they will then call in the officer when they are ready to do your trial. Officers do not all show up in the morning anymore; they are called in on a needed basis.
So, you need to make up your mind BEFORE going in to court. If you decide that you want to play games by telling them first thing in the morning that you want a trial, thereby making them call in the officer, and then think you can simply plead guilty when the officer shows up, you may be in for a surprise. You see, before you are arraigned (i.e. plead), the prosecutor will notify the court that they plan to amend up the speed. The JP will know that you asked for a trial when you spoke with the prosecutor that morning, so they may not be willing to accept your guilty plea to the charge as is since you've waste time and forced them to call in the officer. The JP sometimes will say lets run the trial since the officer is here anyway! At that point, the trial is run and the amended speed rate could be accepted by the court.