The rest period on transatlantic flights has been halved from 24/20/17 (depending on route) hours to 12 hours. This means that staff can do the outward flight to, say, New York and then work the flight back to Ireland that evening.
Um, I don't think so; according to the schedule the morning flight from DUB-JFK departs 10:45 and arrives 13:15, while the late flight back departs 21:45 arrives 09:45. Even with a twelve hour rest period you're guaranteed an overnight on that one.