Just assign TDateTime to OleVariant.
I doesn't work.I found solution sorry for my fast question.
Datetime must be formated like YYYY-MM-DDTHH:MM:SS(+-)HH:MM
so i wrote Function to convert TDateTimePiscker or any datetime class to right format because
olevariant can handle string and pass to right format
function TForm1.SetTime(DateTimePicker: TDateTimePicker): string;
var
date: ShortString;
time: ShortString;
begin
DateSeparator:='-';
date:=FormatDateTime('yyyy/mm/dd', DateTimePicker.Date);
time:=FormatDateTime('HH:MM:SS',DateTimePicker.Time);
Result:=date+'T'+time+'+01:00';
end;
end.