It isn't a fail-safe way of guesstimating but... between 10.25 and 11.30 am on Friday this week there are 28 flights departing Dublin. Of those
7 Ryanair Boeing 737-800 (with ~180 seats)
5 Aer Lingus Airbus A320 (with 174 seats)
which is about 2000 seats between them
8 transatlantic flights with various carriers but guesstimate a minimum of 300 passengers each giving you another 2500 passengers (probably more)
another 8 flights with 80+ seats apiece so say another 1000 passengers (again probably more.)
so say there are 6000 people who prior to that window have to be processed through checkin and security and for the transatlantic flights through CBP (if you are flying stateside you need to leave sometime for this as it can get quite congested). As a previous poster suggested if you can check in online then the main queue to worry about is security. Getting there by nine you should have no problems. I have found that it can be both a breeze and a pain so it is always best to be on the safe side. Having said that it isn't the worst time to try flying out of Dublin.