For the last 10+ years, both I and the little lady have worked for employers that took the attitude of "as long as the work's done on time, we don't really mind the hours you work". There were some rules around it - core hours of 10-12 and 2-4, where you were expected to be at your desk, and you were still expected to meet (and probably exceed) your contractual weekly hours, but, say, if you wanted to get away early then it was accepted that you could, as long as you made the time up. Or, if it made for an easier commute, you could do 8-4.30 or 10-6.30, or whatever. This flexibility worked both ways - if the proverbial hit the fan, you were willing to pitch in and stay to sort it out.
Is this unusual? I ask as the little lady has just started somewhere that is incredibly prescriptive in the hours to be worked (9-5.30) and there is no flexibility. A guy who works away from home in the week is allowed to leave a whole half hour early on a Friday, as he has a 4 hour train ride home, and that's exceptional apparently.
My gut feeling is if someone says 'you must work these hours, and we won't give any flexibility that might help you out' then my response is 'okay, I will work those hours, and there'll be no flexibility from me either'.