Chlorine is chlorine so you dont need to let it disipate before using another type. Granular chlorine contains CYA (dichlor) and calcium (cal hypo). So...if you have high CYA and/or calcium levels, its not advised to use that form of chlorine. Liquid chlorine (aka bleach) is the prefered method to shock. I also will ask why you need to shock on occasion. Do you get frequent algea outbreaks? If so, there is something else going on you need to address. Do you have test results you could give us? pH, TA, FC, CC, CYA.