When a patient with hypertension takes a particular type of blood pressure medication, the effects on the systolic pressure, S(t), can be measured by the following piecewise defined function: S of t is equal to the piecewise function of 140 minus 6 times t if 0 is less than or equal to t is less than or equal to 4 and 116 if 4 is less than t is less than 8 and 96 plus 8 times t if 8 is less than or equal to t is less than or equal to 12 where t is the time, in hours, since taking the medication. Based on the graph of the piecewise function, if the patient takes the blood pressure medication at 8 a.m., in which interval will their systolic pressure be lowest?