Resource assignment ETC is not adjusting based on changes made to the Resource calendar if the resource was assigned to the task before the calendar change was made in PPM. This change includes marking days set as working days as non working days.
This is working as designed. In order to see the changes in ETC distribution, you would have to autoschedule the project. This can be done by running the Autoshedule Project job in PPM->Home->Reports and Jobs or going to the project gantt and running autoschedule there.