Sql doesn't care about format unless you're returning the DateTime 's value as a string instead of a
DateTime
(you should generally avoid returning a DateTime as anything but a DateTime). The front end is where you control the format (how it's displayed). You can do that like this:
using System.Threading;
System.Threading.Thread.CurrentThread.CurrentUICulture.DateTimeFormat.ShortDatePattern = "dd/MM/yyyy";