I'm thinking of taking a transatlantic cruise, one in the spring to Europe and then one in the fall back to the USA, but flying to and from the US on the other part of the journey. My question is: what is the amount of time the airlines will allow you to book a flight, meaning does the return have to be within six month or twelve months?
As long as you book it all at once, it's whatever the booking machine will let you do. It's essentially just a round-trip operation with different points as far as the time limit goes. You probably couldn't buy a ticket from home to London with a return two years later - - that kind of idea. Also, you don't have to have any of the same airports on the journey. For example: you could go from Columbus to Rome and come back from Porto to Savannah. You could also tag on a Savannah to Columbus leg. You can also come back through the same place and keep going, for example: we sometimes go from Florida to Europe, then from another city in Europe to Argentina, then to Florida, then to Asia, then from another city in Asia to Utah. (This is not to imply we keep moving the whole time - - there's some long times in there for both Florida and Argentina.) There's a limit to the number of legs, I think, as well as the time limit to get the whole thing done. You can also nest another open jaw in the middle somewhere if you start to get limited by legs.
I may be wrong but I think the only restriction would be how far in advance you could buy the one leg ticket, ie: you couldn't buy the first leg now and the return leg next year sometime (more than the 12 months away or whatever the max is for purchasing a ticket). In other words yes you could buy an open jaw from LAX to JFK in May, sail to Europe and then sail back from Europe to Miami and then fly from MIA to LAX in Sept, all booked at one time. Just an example. Hope this makes sense.
I will not swear to it but believe it is something like 330 days - abut 11 months. I think that is about earliest you can make a reservation. In other words, I don't think I could make a reservation to go for Aug 15, 2014, today. But could I make a reservation for June 1, 2014, with a return on Sep 1, 2014. Interesting question. I will have to experiment with some dummy bookings. Follow up: I played with a couple of search engines. The furthest out I could make a reservation was exactly one year. And that also applied to the return leg. You might call the airline direct and see if they have any suggestion for booking more than a year out.