Project does not know of any modified working schedule unless you tell it so. The default calendar used in Project for scheduling is the Standard calendar where work is defined as 08:00 - 12:00, 13:00 - 17:00 Monday through Friday.
When you enter a duration of 9 days - project will count 9 working days based upon the calendar. So if the task starts on Monday March 17 it will end on Thursday March 27.
You need to modify the calendar (Change working time) and then you will see the gray shade in the Gantt chart showing the changed working time.
If you need more details on changing the calendar, post back.