What does com.ibm.team.build.BuildResult.buildStartTime represent in BIRT from the LIVE_SNAPSHOT data source?

I am working on building a BIRT report against the live Build Results data.  I would like to display the start time of the build in my report.  In the data set based on the Build Results live data (com.ibm.team.build.BuildResult) there is a column named 'buildStartTime'.  This seems like it would be what I am looking for, however I am not sure what it actually represents.  When adding the data set to the report the column is displayed as an integer.  The values that are presented are both positive and negative numbers. 

Can anyone tell me what this value is and/or how to obtain the time the build started?

Thanks,
Jamie.