[arch-general] how to give Date&Time root priviledge

Hi all, I use kde4.7. As the time zone does not set correctly, I tried to change the timezone as "America/Toronto" in rc.conf. it did work but the time still not right. So I used date&time --KDE control module to adjust time, it said 'System policies prevent you from saving the date/time setting', and asked me input the password for root. The authentication failed, I am quite sure the password was correct. I guess I didn't add time in user group. Any solution about this? Thanks a lot. Adrian