%!demo
%! ## `exceltime` returns an Excel serial date number.  The `'1900'` system is
%! ## the default; pass `'1904'` for the Excel 1904 system.
%!
%! t = datetime (2024, 3, 9, 6, 0, 0)
%! exceltime (t)
%! exceltime (t, '1904')
