As teaching is a profession, it can never be regarded as a straight nine to five job. However, as the recent workload agreement has made clear, there are limits to what a teacher can do and schools should consider work-life balance issues when determining timetables.
As a teacher, you are required to be present for the 190 days pupils are in school plus five other days. Overall, your normal on-site working year is 1,265 hours, or an average of 32.4 hours a week. As we know, all teachers work far more hours in term-time and for more than five days when pupils are not present. Within these parameters, a school can set its own pattern: one facing a difficult Ofsted might have more staff meetings than in a normal year.
As to starting and finishing, times must be reasonable within the framework of the 1,265 hours.