I did this last week from AA to RyanAir in under 20 minutes. [I only had carry-on for the AA ORD-DUB sector] but size restrictions meant I had to check-in for RyanAir. Check-in does not open until 2 hours before so I had 20 minutes to hang around and review their procedures.

Although there were lines for all departures, the RyanAir check-in was very effecient, for example the line adjacent was for Valencia with 3 Desks, but as soon as they saw the line was growing they opened a fourth desk to assist. I believe that although final check-in is 40 minutes before departure, from my observation they seemed to do everything to ensure nobody was in line by the 40 minutes closing time.

The security line at 9.30am was nil, and even though Dublin had thick fog and all flights were delayed we were kept fully informed.[Take a note AA]

Remember you can't do OLCI if you have checked bags. But you can still do Priority boarding by paying a fee at the check-in desk.