Having worked outside teaching, and in teaching, I can't quite get my head round the fuss that is made (tbh, only on here, never by teachers in the real world) about the precise hours stated on a contract.
When I worked as a manager in industry, my contract said that I was supposed to work from 8.45 until 5 pm, with a half hour lunch break.
Nobody did, and nobody expected to. Nobody brandished the paper and said 'I'm only contracted for these hours', everyone did what was needed for the job that they were doing. 8.30 to 6 or 6.30 is, I would say from my experience and acquaintance, the 'normal' working pattern in graduate employment - a 10 hour day, very similar to the hours (though not the precise timetable) of many teachers in term time.
Professionals in all walks of life do the hours they need to to do their jobs. The hours that they need to do that work will not, in general, match the precise wording on their contracts. That's how it works. For teachers to be so fiercely protective of their 'contracted hours' reflects badly on them, when the reality is that virtually everyone in a 'graduate-type' job works for longer than their contracted hours.