At 12hr, total phenolic compound were the highest, but for 24hr physiology of plants were more than 12hr. As the result, phenolic compound changed some physiological functions in plants as following; accumulate cell vacuoles, or polymerize into lignin, which strengthens the secondary cell walls. [Valentine et al., 2003] So if you want to phenolic compound produce any more then, you choose select the 12hr method.