The timeline should show a tick mark on the timeline bars where the first response was received from the server. Right now the timeline bars show the start and end times. The start time is when the request was sent, and the end time is when the load finished. So the first response time would help show how long the actual data was being transfers, and help show delays between start and first response. THis should be easy, since the WebInspector.Resource object has the responseReceivedTime time property.
*** This bug has been marked as a duplicate of 14258 ***