All of the pick up times are between 11:30 and 12:30. You will be given a specific time to meet on the last night of your resort stay. You'll also get luggage instructions--basically, have your luggage ready for pick up at 8 am.
You will arrive at the port at about 1:30. Each bus serves 3 resorts; you won't know whether you are the first or the last pick up till you see your time.
It is cheaper to do a one way rental if there are 2 of you. I can't say that I've done a rental + gas + tolls for under $35, but I can usually bring it in for $45! That gets me to port on MY time schedule, but is a little more effort (picking up and dropping off car, dealing with luggage myself.)