Beijing-72 hour rule

Hi I am a US citizen. If I arrive to Beijing from US on a Monday at 8 am. According to the rules for Beijing the 72-hr duration start at 00h01 following day of entry, which is Tuesday. So my flight to Japan can leave anytime on Friday before midnight, such as at 9 pm. Even though my stayed totaled of 85 hours, this is still acceptable, is this correct?