Is it unprofessional to request a schedule change before starting the job?

I’m a high schooler and recently got offered a job as a tutor/assistant at Kumon. I have not started the job yet, but on Monday, I’m required to work from 3:30PM to 6:30PM. The thing is that I have a club from 2:30 to 3:30 probably won’t get to work until 3:50 or 4:00. Would it be okay to ask to start work later (preferably 4:00) and work overtime or would it seem unprofessional?

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