Not directly an answer to your request, but you can graph the log (hotspot log and other) using a third party syslogger like Splunk.
Se link in my signature for how to use Splunk with MikroTik. There is an hotspot user view.
Direct link to the hotspot view
http://forum.mikrotik.com/t/tool-using-splunk-to-analyse-mikrotik-logs-3-3-graphing-everything/121810/1