Ok. I've got my own solution, but is there another, better way to solve it?
var
T1, T2: TTimeStamp;
theDate: TDateTime;
begin
T1 := DateTimeToTimeStamp(DatePicker.Date);
T2 := DateTimeToTimeStamp(TimePicker.Date);
T1.Time := T2.Time;
theDate := TimeStampToDateTime(T1);
end;