@Annie - Before you worry about the small details of your plan...are you really sure you want to go to all that trouble to get to...Killarney?
I ask because, well, here's what Rick Steves has written about Killarney:
Listed as #6 on Rick's "Top 10 European Tourist Traps"...
Killarney (Ireland): This is a place where most tourists wear nametags — a traffic jam of tour buses. If you have the misfortune to spend the night in Killarney, you'll understand what I mean. The town is a sprawling line of green Holiday Inns and outlet malls littered with pushy shoppers looking for plastic shamrocks.
If you are open to input from others, post your plans for your trip to Ireland, and mention your interests, preferences, etc. Ireland is a truly wonderful place to visit, full of great things to see and experience. There are lots of experienced travelers here willing to offer suggestions to help make your trip awesome and the best it can be for you.
PS: I will just add this to your original question: I actually think it's often a smart way to make the best use of your time on an (all too short) trip to Ireland to do exactly what you are proposing: Land in Dublin, then immediately move on to a destination away from the big city. You'll be jetlagged and tired on that arrival day, so that day is usually a wash anyway, and moving on to somewhere else can make a lot of sense and help you efficiently get more out of your time. Sleep deeply that first night, wake up refreshed, and really begin your trip the next day. I'd just question whether Killarney is that place. I can think of better places, but that depends on your overall plan, and it's your trip, your decision.
Hope some of that helps.