Channel Casting (Su): At 2nd level, a soul warden can expend a use of his channel damage ability to spontaneously cast from a select group of spells. At 4th level and every 2 levels thereafter, a soul warden gains access to a number of additional spells he can cast in this manner. The spells a soul warden can cast with this ability (and the soul warden level necessary to cast such spells) are listed below.
You are expending uses of channel damage. You are not actually using the ability, so the speed at which you can normally channel energy is irrelevant for this purpose.