Release Date for A PO

Hi,

Is there a transparent table where i can retrieve the release date (po approval) of a purchase order?

my client want to display in the report the po no, po date, and the date the po was release/approved.

any help... my last option is to use the table chdr but then again this will be variable coz depending on the changes done in the PO...

appreciate all help , points will be given.thanks in advance.

rgds,

she