Directory Server has access logs that are producing timestamps of operations (ie connections, bind request, bind response and connection closing). Please include extract of them here.
DS also has error logs that are indicating errors or warning related to special conditions. Please check.
Finally, it may help if you give more insight on which OS you are using, which LDAP library is providing the ldap_simple_bind_s method, whether SSL is used...
Regards,
Ludovic.