Not sure what you mean by pre-booking bags in. The Aer Lingus bag and tag? Is this possible going to US?
My checked in luggage has been searched while waiting in the queue for check-in (admittedly this was about 2-3 years ago).
Anyway - personally I would allow a minimum of two hours (and I'm someone who usually cuts these things fairly tight) - as you'll have to clear immigration as well.
If there are several US bound flights scheduled at around the same time as yours then allow more time as the queue for immigration will obviously be longer.
if your travelling aer lingus to NY and not able to check in on line , then let me tell you,, before 6am in the morning there is no check in staff, not even to take the bags for the bag drop desk, you must wait till 6am for the staff to come in,, and the flight leaves at 645 for dublin and onwards to the usa then,
SNN is nice , and an easy airport to navigate, get thru