My mistake, main problem solved.
Spaces are not allowed in ldap queries. In fact, I didn't get "no result", I got one message "Bad search filter" that was not handled correctly.
I changed my filters so that it now uses the createTimeStamp and modifyTimeStamp attributes. Using "(&(objectClass=groupOfUniqueNames)(modifyTimeStamp<=20091224))", I retrieve the entries that haven't been modified since 2009/12/24.
Caution : this filter cannot be applied to the entryCSN attribute as it makes OpenLDAP shutdown.
If by "shutdown" you mean "crash", that might have been true for 2.4.7, the version you claim to use. That version was released 31 months ago. The current release does not crash. Of course, bearing with malformed filters is not the main reason you should upgrade.
p.