Getting elapsed build time from REST API

Hi

I'm working on a project that needs to get the time a build took to complete (including tests) from the TeamCity REST API.

Unfortunately given I need to specify the different fields I'm requesting, I can't work out which field I can use to get the elapsed build time in seconds. I've seen references to "elapsedSeconds" in places, but have had no luck.

At the moment my request looks like: http://teamcity/app/rest/builds?locator=buildType:(id:my_id_goes_here)&fields=count,build(buildTypeId,finishDate,status,statusText,webUrl)

I think getting the elapsed seconds would look something like: http://teamcity/app/rest/builds?locator=buildType:(id:my_id_goes_here)&fields=count,build(buildTypeId,finishDate,status,statusText,webUrl,running-info(elapsedSeconds))

The request above succeeds, but the responses I get don't include the elapsed seconds.

Can somebody point me in the right direction? And is there a listing of the different fields available in the REST API for different types of objects?