Three taps A, B and C can fill a cistern in 20, 24 and 30 hours respectively. On a given day, tap A is opened at 6:00 AM to fill the empty cistern. Tap B is also opened after two hours and tap C is opened another two hours later. When all three taps have been opened for two hours simultaneously, tap B is required to be closed. The minutes from start, after which tap A should be closed so that the cistern is full at 8:00 PM is….