Banner Manager Dates

I have a couple of questions regarding the banner manager. If you are running a banner for the a certain month only, would you set the Expires On date to the last date of the sale month OR the first day of the following month?

Also, it there a reason why the dates in the banner manager dd/mm/yyyy instead of mm/dd/yyyy like the rest of ZC?

Thanks!

You would set the date to the last day that you wish to see this banner ...