Perhaps BA are willing to sell EI a slot at that time? But I can't think that's the case as that's when most of BA's fleet leave in the morning. TBH, I can't see many passengers wanting to go from LHR to DUB at that time, I think it's probably quite likely that this route may have been losing money for EI. If it was a 6:50 arrival slot and 22:50 departure then I imagine EI would have a big use for it, but not the way it is.