Here we go again with this mess_stats_job. ;-)
Back to the original topic. I just though that it might be useful to check on DBMS_ADVANCED_REWRITE package and see if you can use it to incorporate certain hints that can make parsing fast.
It appears that one of the 20+ tables was analyzed last night (by the gather_stats_job) and that invalidated the plans. Apparently this is
-- Best regards, Alex Gorbachev
http://blog.oracloid.com -- //www.freelists.org/webpage/oracle-l