Time Sheet Report takes an excessive amount of time to display

Summary

Using the Time Sheet Report on certain instance configurations will take an excessive amount of time to generate. This is causing timeouts on our ngnix proxy in OnDemand and renders the plugin unusable for our customers.

Environment

JIRA 6.0-rc1 PostgreSQL Internal Directory

Steps to Reproduce

Install JIRA 6.0-rc1 (can be downloaded from http://www.atlassian.com/software/jira/download-eap)
Restore the provided XML backup. This is demo data created with our data generator and has evaluation licenses loaded. Login / pass is admin / sphere.
Install the timesheet plugin.
Browse to a project and attempt to generate a time sheet report.

Expected Results

The report configuration screen appears within a suitable timeframe.

Actual Results

The screen takes 11 minutes to generate. See attached image.