When a task calendar is applied to a task, the task isn't scheduled correctly or as you expected.
If you create a calendar for a task and later assign a resource to the task, the task may be affected by nonworking time in a resource calendar. Microsoft Office Project 2007 schedules tasks based on the project calendar, and then by the resource calendar (if a resource is assigned to the task).
If a task calendar is applied, Project ignores the project calendar. Instead, Project schedules the task based on the task calendar, and then by the resource calendar (if a resource is assigned to the task). You can choose to ignore the resource calendar when scheduling the task, but be aware that this may allow work to be assigned during a resource's nonworking time.
To schedule a task by using only the task calendar, select the task, click Task Information , and then click the Advanced tab. Select the Scheduling ignores resource calendars check box.