Hi Yellow Sun,
For the purpose of claiming compensation, it's the arrival time that matters
AFAIK, not the departure time. Looks like you arrived roughly 7 hours late.
From my rudimentary understanding of the relevant regulation it seems you're eligible. If BA still refuses to play ball, there are plenty of BA crew / staff on this site (I'm neither).
I may get flamed mercilessly for saying this
but many BA employees, especially pilots, are often happy to help pax where they seem to have been short-changed - it doesn't take them much time, BA keeps a customer, management are happy, etc.
If you get nowhere, feel free to send me a PM. Good luck!