Can you provide a detailed explanation of workflow timing diagram?

Looking at the workflow diagram, I see for each call a multi-colored bar describing the changing state of a job (called task) on FireCloud. The GUI makes it difficult to get information on each of the states (e.g., sometimes the leftmost portion of the bar is associated with "Pending", other times it is associated with "PreparingJob"). It may be that both states and the transition between the two is captured, but one or the other is so short it is impossible to click on it. Regardless of the graphical display, however, I would like to know what each of these states means.

Using the API, I was able to see that the API returns a sequence of execution events for each call, e.g.,

    "executionEvents": [
      {
        "startTime": "2017-01-10T17:19:59.284Z",
        "description": "Pending",
        "endTime": "2017-01-10T17:19:59.284Z"
      },
      {
        "startTime": "2017-01-10T17:19:59.284Z",
        "description": "PreparingJob",
        "endTime": "2017-01-10T17:19:59.286Z"
      },
      {
        "startTime": "2017-01-10T17:19:59.286Z",
        "description": "RunningJob",
        "endTime": "2017-01-10T18:02:50.113Z"
      },
      {
        "startTime": "2017-01-10T18:02:50.113Z",
        "description": "UpdatingJobStore",
        "endTime": "2017-01-10T18:02:50.124Z"
      }
    ],

I'm guessing that it is this information which is depicted in the workflow timing diagram. I'd like to know what each of these states means. In particular,

(1) Is the call in a pending state prior to the creation of the VM Instance? What causes a call to remain in a pending state for a long time?
(2) Does the call state move to PreparingJob when the VM instance is created? What is happening while the call is in this state? I don't think file localization occurs when in the PreparingJob state because typically the call remains in the state for too short a period.
(3) Does the RunningJob state also cover file localization times?
(4) What is going on in the UpdatingJobStore state?
(5) Is the time we are charged for the time we are in the RunningJob state?

We would like this information to assist the benchmarking and workflow optimization work we are doing. It would be very helpful if we could get answers to this relatively quickly.

thanks!