Well legally I assume you are owed these hours and so it it bothers you that much then you can point it out and make a request.
Will it make you "that person"? Absolutely. But I guess it depends what you want. Some people the job is just a job, the hours lost will feel like a big deal .
The thing is, most people who work in a school do so for more than just the money, my own kids school most members of staff are in before 8 and leave around 5, that often includes support staff who are not paid to be there. School trips the staff volunteer for, the last one was a 730 start and a 10pm finish, our PTA events are heavily supported by staff including support staff.
Don't get me wrong we have some staff that have childcare to consider and leave earlier but everyone pulls their weight, not for the pay, not for the job, but for the children, they want to make everything special for the children.
However, our staff are supported and there is definitely a flexibility within the job, staff able to leave for appointments or to see their children in concerts etc, so it's swings and roundabouts. If your not getting the same flexibility then I do understand your frustrations.