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We did this last December. Took the printed email with us to the ticket window on our first park (ours happened to be Epcot, but you can do this at any park), IDs as well, and the lady there loaded the actual tickets onto our Magic Bands. We all did it together at the same time though, it was very easy and didn't take more than 10 minutes - not sure how it'd work if your family did it a day earlier than you! They might be able to get it done for you and be able to hand you your MagicBand the next day, ready to go?