Non-US Datetime Format Switch in Nurture Program

I'm running a Happy Birthday nurture program, and have set my Date/Time format to DD/MM/YYYY in my account settings and instance. My customers DOB have also been synced in this way too. However, when it comes time to send the triggered birthday email, Marketo is reading the format as MM/DD/YYYY, so the wrong people are receiving birthday emails.

Are there other settings I should be changing??