How to handle upcoming family event during application process?

I've applied and interviewed for a new job. I am in a close family members wedding out of state in January. I was nervous and failed to mention this in my interview. It would require me taking 1-3 days off depending on their scheduling upon hire. How do I best handle that at this point. I know it could be a deal breaker, but I have committed to it.

Would it be presumptuous to contact them and advise them now? Or is it rude to wait until an offer of employment is made?

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