I think anything before Friday would be optimistic. I've online banking with several different banks, and in my experience BoI has always been the slowest, with 3-4 working days as standard, even to other BoI accounts. I'm afraid I can't comment specifically on international transfers. (I found Halifax the fastest; never more than one day and on one occasion the same day to external accounts, and immediate transfer to Halifax accounts. I'll miss them.)
The cynic in me says BoI like to have that extra few days when the money is 'between accounts' to make a few extra € profit. Scaled up to all transactions, I'm sure it's significant.