Date Sensitivity

Hello. I am currently inquiring whether the Date Sensitivity is pre-set or if I need to pre-set my entry dates? If I do need to do so, where would I be able to change this information? I need the dates to reflect month/day/year in a consistent manner, and it has been brought to my attention that the dates are not consistent for the sales orders. This makes life difficult when viewing due dates for days 1-12 as there are 12 months in a year.