hi Rebecca,
to me you can do any time that works for you and your students. when I have done my trainings I have done different times such as noon to 7 and noon to 8. the only thing about 9-5 if your students want practice sessions in the morning and a questions and answers portion for the test when would you slit that in. would you be giving them a lunch break which would cut back on the time for teaching or would you inform them to bring lunch and snacks with them and work through lunch. I know of trainers that did 9-5 and it worked out lovely.