As a newbie to Project, I am having difficulty with my calendar working time.

My project has some task that operate under a normal work week with others operating on 24 hour basis. When I change the calendar on an individual task from the default Standard calendar to the 24 Hour Calendar, if appears to me Project uses the work times from the Standard calendar to display the duration of the task on the Gantt diplay. That is, a task that is entered as 3 days only displays as one day (I assume (Yes, I know what assuming does. But it's just me in this case.) the one day is the result of the 1:3 relationship in the working hours in a workday in the Standard Calendar versus the 24 Hour Calendar).

Might someone shed some light on how to get my project to honor the two different workdays?