otp.config.locale.time.date_format = "d/m/y"; (to be extra thorough, you can also override your chosen locale's date_format, ala otp.locale.English.time.date_format = "d/m/y").
BTW, there are two other date / time related format fields to be overridden (and changing those should change date / time formats across the web app):
otp.config.locale.time.format = "d/m/y @ H:i";
otp.config.locale.time.time_format = "H:i";
Take care,
Frank