If we fly the day of the cruise we leave NY about 7:00 am...which puts us into the Orlando around 9:30 or 10:00. Your arrival time of 10:40 should be fine that day. I would worry about anything that got them to Orlando after 1:00 or so, because everyone must be onboard the ship by 3:30ish....
I agree that there are added costs of flying in the day before but sometimes it is worth it. But, since they are only coming from Washington, D.C. (and not from CA) they should be fine.
Hope they all have a great trip.
MJ