Will you have checked bags? If so, what are you going to do with them? (Remember, you can't check them LHR-DUB-LHR-XXX.)
And am I right in thinking that this will be during the northern winter season? (That's when I can see a BA arriving at DUB at 0800.) If so, have you allowed for the possibility that the time of the DUB-LHR may yet change between now and then?