procedure THRForm.Button1Click(Sender: TObject);
var
  D:TDateTime;
  s:string;
begin
  D:=VarToDateTime('05-10-14 04:35PM');
  S:=FormatDatetime('YYYY-MM-DD HH:MM:SS',D);
  showmessage(s);
end;

function SetFieldDate(str: string): Variant;
begin
  if str = '' then
    result := Null
  else
    result := StrToDateTime(FormatDatetime('YYYY-MM-DD', VarToDateTime(str)));
end;

1 function SetFieldDate(str: string): Variant;
2 begin
3   if str = '' then
4     result := Null
5   else
6     result := VarToDateTime(str);
7 end;