I am using the built in time tacking. I have a sprint with one task. This task has an estimate of 4d. every day I log work and the remaining time on the task deceases as expected. The estimation field is 'Time' but the burn down chart does not decrease.

Just below the remaining work it shows 'Number of story points left to complete this sprint' How do I change that to show the time remaining. I am not using story points.
I would like to see the overall time remaining reduce every day where I have logged time or changed the remaining estimate.