Thank you all for your very prompt replies. I quite understand the sensitive nature of my question and why some might wish not to respond - my apologies.
I came across the following post (albeit 8 years old) on another Forum which was signed: 'My career experience as an airline pilot with an ACARS'. I wonder if anyone could confirm whether or not the main cabin door opening simply transmits the parking brake time (in time) not the door opening time or have their been changes to the ACARS whereby the Door Opening time is now signalled. Thanks.
‘The OFFICIAL times are generated by computer when certain things occur on the aircraft. Almost every airliner large and small these days is equipped with an Aircraft Communication Addressing and Reporting System (or ACARS) .
http://en.wikipedia.org/wiki/ACARS
This computer transmits the "out", "off", "on" and "in" times for the flight. The "out" time starts when the captain drops the parking brake with the main cabin door closed. The "in" time is recorded as the last time the parking brake was applied. The main cabin door opening sends a signal that transmits the "in" time. Unless the captain reset the brake while waiting for the door to be opened, that time is what is recorded