From the Bus Eireann website, I see that there 100X and 101 services are PICK-UP only at the airport. So I am ruling them out.
From the Dublin Bus website, I see that the 747 journey takes an estimated 35 mins. If I assume the worst, we'll say 60 mins.
Departure at 3:10, into airport at 4:10, go straight to check-in Fastpass machine.
Though I now see that the check-in closes 45 mins before departure, that's at 4:25pm. It'll be tight!!
Hmmm, but now I see from the Aer Lingus website that I can check in online. I'll look into it.