Excel uses the Windows short date format in headers/footers.
Very little formatting can be done with this.
Couple of options......................
Either enter the date as text or use VBA to change the formatting to what
you wish.
Sub DateInFooter()
With ActiveSheet
.PageSetup.CenterFooter = Format(Date, "mmmm dd, yyyy")
End With
End Sub
Gord Dibben MS Excel MVP