My shift in LTC is 2-10pm, and honestly, the only "slow period" of my entire day is between 230-400 (after water and snacks are passed). Within that hour and a half, I begin charting (thank God for Caretracker), strip beds for those who are scheduled to take a shower, answer call-lights, get weights, and begin taking orders for those who eat dinner in their rooms. Dinner is scheduled for 5pm, so once 6pm hits, there are 10+ Residents asking to go to bed. In my facility, there is no time to sit, and I am fortunate that the majority of my co-workers are always focused on the job. While some do have a tendency of ducking in the shower room to play with their cell-phones for a few moments, nobody outright sits around and blatantly does nothing.
Does your facility pass out line-up sheets? I would make it clear to whomever is in charge that the line-up should be adhered to in the instance of charting only, unless of course the other CNA finishes their work around the same time period. If one of you is putting 10 people to bed, and the other only 3-4, that is a problem.
I believe that CNAs should be responsible for other CNAs. All of us in the workplace have a common goal, the comfort and health of the Resident. If you are unhappy with the quality of work your co-worker is demonstrating, approach them professionally, give them the opportunity to change before going to management. It's your license after all, right? :)