JD
The JFK terminators were added, and the departure time changed, at about the same time as the BA591 service was extended to Melbourne (mid 1970?). In 1969 the only daily JFK services were the BA501, BA505 and BA509. In 1973 the departure time from LHR became 1300 but now the Monday and Saturday service terminated at JFK. The arrival time at Sydney was 1030 and at Melbourne was 1300.
Of the 15 BA591 LHR departures in my logbook the earliest is 0950 (sched 1000) on 23/2/72 and the latest is 1303 (sched 1300) on 26/3/73.
Dave