Hi bjhs,
the correct perl syntax to sort the pivot-field is to call method "AutoSort" and provide the first two mandatory parameters, like:
$workbook->ActiveSheet->PivotTables('PivotTable1')->PivotFields('Day of Month')->AutoSort(2, 'Day of Month');
#Const xlDescending As Long = 2
Further information can be found here:
http://msdn.microsoft.com/en-us/library/office/ff834371.aspx
best regards,
ejp