"Scheduler Delay" of a task is confusing

Run the following code and check the UI

sc.makeRDD(1 to 1, 1).foreach { i => Thread.sleep(30000) }

You will see "Scheduler Delay" of a task is almost the same as "Duration" until the task finishes. That's really confusing.

In Spark 2.2, "Scheduler Delay" will be 0 until the task finishes. This is also not correct but less confusing.