Birth date question for the bday coupon

Hello,

So I want to buy a bunch of Santa containers, but I’d like to use the bday coupon to get double. I had set my birthday last year to January 18th. However, I’d like the coupon earlier. It says the earliest I can change it is January 2nd. If I change my birthday on the 2nd to the 3rd of January, will I still get the coupon that day, or will it only give it to me after the 18th which I had set previously? Thanks so much!