Fuhrman's assumptions were based on the narrow timeline that would indicate they got rid of the body almost immediately after she supposedly died. The fact is they could have had much longer than that to dispose of the body of PVDS came and picked Urine up with the body. They would have had somewhere between 2:00 am and 6:30 am. Four and a haf hours.
Someone mentioned earlier that daylight would have occured earlier than 6:30. Seem like Greta commented on it, just don't recall what her final timeline was.