PHILADELPHIA (CBS) — The Philadelphia School District is defending changes to its school start times, but some parents say the new times are disruptive.

For some students in the Philadelphia School District, the bell will either be ringing earlier or later than normal when they return for the start of the school year.

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“We collaborated with schools and then made the final determination. You will see that some high schools are starting earlier, some are starting later,” Dr. Evelyn Nunez, chief of schools, said.

School officials say the vast majority of elementary and high schools will see minimal changes in arrival and dismissal times of less than 30 minutes, but some parents say every minute counts when it comes to a disruption of family schedules.

“My elementary school was moved to a 9 a.m. start time, and like a lot of other parents, I really don’t have any idea how I’m going to be able to get to work on time if that happens,” Stephanie King said.

“I think once people get their actual schedules, it’s going to cause even more chaos,” Philadelphia Councilmember Helen Gym said.

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Gym and a group of 10 state legislators are asking the district to rethink the bell changes for the upcoming school year for the sake of student safety and well-being and preserving parents’ jobs.

“Especially high schoolers, who are now being asked as much as 45 minutes to an hour earlier, which means that they could be on public transportation when it gets dark to elementary school children, some of whom are often up at the crack of dawn and who having working parents who really need them to be in school at an appropriate time,” Gym said.

School officials defended the need for school bell time changes setting a need for uniformity.

“Within the district, we have some 30 different arrival and dismissal times,” Hite said. “When you’re trying to coordinate a transportation system with that many arrival and dismissal times that are different, you limit the opportunities you can use a bus.”

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District officials say they’ll be providing support for parents and schools to help adjust to the changes.