How is a cardioversion administered?

With paddles. The patient is sedated in preparation for the shock. Paddles are placed on the chest once the patient is asleep, and a properly timed shock is delivered to restore normal rhythm. Sedation is allowed to wear off.
Depends. In emergeny, it is given as soon as possible to save life. During elective case, patient will be sedated and comfortable, before electric energy is delivered through pads on the chest wall. Most people do not have pain or remember the electric shock.
Cardioversion. Elective cardioversion usually takes a couple of hours with pre procedure, procedure and recovery from anesthesia. The actual electrical cardioversion is an instantaneous shock. The periprocedure and recovery is what takes the bulk of the time.