In my RTC project area the work item progress is configured to show the time spent . I want to change this to time remaining.

I have a sandbox RTC project area, where I tried to change to from time spent to time remaining, but when I save the project area, it is switched back to time spent. Isn't it possible to change this or is it my access that doesn't allow me to change it ?

If there is an open task, where the owner has filled the time spent field with 2 hours then be understood as 2 remaining hours after the project area has changed.