13 hour layover in Dublin

My idea is that this is a particularly bad idea....

I could see going into Dublin or Belfast in that amount of time. I think you will spend a great deal of time on the bus and not experiencing anything of Ireland or Northern Ireland on a 5 hour tour.

I would stick with visiting Dublin.

What time of day do you arrive and depart Dublin Airport?

Don't sign up for a tour. You never know if your arriving flight may be late, or there may be a crowd of other passengers going through passport control. You could, though, take the bus from the airport into Dublin and see some of the main sights around the city on your own.

Make sure you plan to be back at the airport well before the time your airline advises for the flight to Rome. Again, you never know if there may be a traffic jam or other delay, so don't cut it too close.

Thanks for the help. It may not work out anyway.