24 hour flag in Depart/Resource Definition

We have a requirement that 24 hour available flag is enabled in Department/Resource Definition for some resources.  But If do this, the systems calculates the capacity as 24 hours and shows this 24 hours available capaicty in scheduler work bench while that is not the case.  The resource works only 12 hours a day, but may be called to work any time.
Any ideas how I can address this situation?

Thanks