I've taken a CNA class in Washington State, not sure if the system varies between states or regions. I took a weekly class the summer between my senior year of high school and freshman year of undergrad that met four times a week that finished in about a month, and was able to receive certification about a month after due to testing and paperwork processing.
Most schools have a flexible array of class types to fit people's schedules that usually fall under three categories: daily (like "regular school"), nights, and weekends. The trade-off is the less classes you take per week the longer it will take to finish the class; daily classes can be completed in one month whereas weekend classes may take two to three months to complete. I don't think there are any schools with one class per week, however. The least you can probably get away with is two.