How much notice in advance should you give employer that you need to leave early on a certain day?

I work in retail and i'm fairly new. I work every saturday from open to close, today is monday, and this upcoming saturday is my dads birthday. I wanted to ask my manager if it would be okay if left an hour or an an hour and a half earlier so i can go to my dads birthday dinner. I was wondering how many days... show more I work in retail and i'm fairly new. I work every saturday from open to close, today is monday, and this upcoming saturday is my dads birthday. I wanted to ask my manager if it would be okay if left an hour or an an hour and a half earlier so i can go to my dads birthday dinner. I was wondering how many days notice i should give for this? Is this a big request in retail or is ok to ask only a few days in advance? I would still work a good 6 or 7 hours that day, and i am not the only person who will be there at closing time so they will have someone else there. Thanks for any advice/insight you can give me
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