Hello Susan,
It's wonderful that you're docking in Dublin during your cruise this September, and it would be even better if you get to visit Newgrange as well!
The trip from Dublin Port, where the larger cruise ships dock, to the Newgrange Visitor Centre takes around 45 minutes
by car, depending on traffic. By public transport it will take over 2 hours because you have to travel to the centre of the city first before you can catch a connecting bus.
Have you thought of a tour with a
private driver or chauffeur? You'll be picked up and dropped off back at Dublin Port at an agreed time, and they could do their best to make sure you're back at 1pm.
It still might be quite tight time wise, while you really want to have the chance to explore everything at your own pace. Are there any other things you'd like to see or do while you're in
Dublin? There is lots of history in this area as well. :)