export NLS_DATE_FORMAT='DD/DD/YYYY hh24:mi:ss';
connect to RMAN
RMAN> list backup of database completed between "to_date('<start-date>','DD/DD/YYYY')" and "to_date('<end-date>','DD/DD/YYYY')";
RMAN> LIST backup of database completed after "to_date('<yourdate>','mm/dd/yyyy')";