ABC News has begun filming a documentary series, tentatively titled “Golden Hour,” at three Boston hospitals. The series is focused on the experiences of patients who arrive at the hospitals with a serious problem — stroke, myocardial infarction, respiratory distress, trauma, bleeding — and the medical intervention that takes place. It’s being shot at Massachusetts General Hospital, Brigham and Women’s Hospital, and Boston Medical Center. Perhaps because cameras will be very much in evidence throughout the filming, which is expected to last through December, MGH has posted a note on its website alerting patients and staff. The series is described as similar to “Boston Med,” an eight-part documentary produced by Terry Wrong that aired on ABC in 2010. Wrong is executive producer of the news series as well.