The EAP Controller stores connections in its own database, but it does not log them with syslog. Unfortunately, the database is only accessible via the EAP Controller's web UI (Windoze way of doing things), which make it painful to search for a certain connection on an arbitrary date. But you could find out how to query the EAP Controller's database externally (Linux way of doing things) so that you could use DB queries to quickly locate user connections in the past.