Depending on where in Ennis? you have 15 to 30 minutes to Shannon so 05.45 ~ 06.00. get into Shannon the driver drops the car and passenger the baggage (15 mins) clear Irish customs (15 mins) Flight to New York (given 9am)? Pre clear US customs (1 hour) Technically ballpark around 2 hours but 3 hours is the general recommendation from the airlines (United?). SNN is far more efficient than DUB.