If you booked your air and transfers through the cruise line, they will not actually make your air bookings until 30 days prior to departure. You can call the cruise line at this time to get your flight information, so you can then call the airline to make seat assignments. Since they buy their air in bulk, they don't actually make the air arrangements until they have a solid number of people flying in for a given cruise.
As far as when to get the transfers, you will be met by a cast member when you get off your flight (assuming you'd arrive the morning of the cruise, if you're flying from NJ). They will direct you to the waiting busses. You don't have to wait too long for a bus. They run pretty much continuously between the port and airport on cruise days. Specific information on where to catch the bus will also be in your cruise docs, which will arrive about 3 weeks prior.
We've booked our air through the cruise line a few times and always found it very seamless and convenient.