The Aer Lingus website is really where you should be going. First of all--if you are flying up to and including April 2 you go to Terminal 4. If you are flying April 3 and forward you will be going to Terminal 5 which is the Jet Blue terminal. The website clearly says you should check in 3 hours before your scheduled departure.
It is hard for anyone to predict time to get through security. Terminal 4 has a new arrangement that is open less than a month, Terminal 5-integrating Air Lingus and Jet Blue passengers--also not sure. Do not forget that 5:30 departure doesn't mean you can stroll onto the plane at 5:28. Gates close anywhere from 20-40 minutes prior to departure.