sysdate-1/24 is not working in rdf reports

Hi all,

Req:  scheduling existing Report  for one hour and which should take last one hour approved Po's.

issue is :report is giving blank out put when i add sysdate -1/24 and nvl for po number from and to  parameters.when i run the query in SQL am getting records.

existing Code:

AND   (:P_po_num_from is not null and :P_po_num_from <= poh.po_num)

AND  (:P_po_num_to is not null and :P_po_num_to >= poh.po_num)

my code:

AND NVL(:P_po_num_to,poh.po_num)>=poh.po_num

AND NVL(:P_po_num_from,poh.po_num) <=poh.po_num