I have first hand experience with this situation. I bought tickets for a week in July. We ended up going a week earlier than planned, so I showed up at the ticket booth at 1pm with my voucher in hand. The CM told me the tickets were not yet in the system and to call Orbitz. I left the window, called Orbitz, who said (after checking with supervisors) that Orbitz could not change the dates, but Disney could and that I had to deal with Disney. So I went back to the same CM, who told me that Orbitz was wrong. Disney cannot change the dates unless Orbitz does it for them. If it's not in Disney's system, they have to get Orbitz to change the dates. Luckily, the CM and her lead were fabulous! They spent over 45 minutes on the phone with Orbitz (being transferred and put on hold endlessly). Finally around 3pm, I received my tickets. It was stressful and frustrating, but in the end we got our tickets, and the CM gave us complimentary FP for our inconvenience! I cried when they offered the FP's because they were the ones who bent over backwards for my error in dates.
If you go later than your dates, you will probably be ok, as at least the tickets will have been released by Orbitz. I also do not know how long they will be in the system. It's a matter of whether or not Disney can still see the tickets and know if they were redeemed or not.
If you go before your dates, be prepared for a lot of hassle. Do not believe anything Orbitz says, good or bad. Disney will have to contact them and get them to release the tickets. I have not read any situations of anyone being able to get Orbitz to release them early without Disney intervening. Do not plan to get your tickets in only a few minutes. Plan to be at the booth for a while, and if you get them quickly, all the better.
This can be resolved, and I haven't read of anyone having to buy new tickets, but I have read (and experienced) a lot of hassle with Orbitz tickets. I doubt I will use them again, even with a monetary savings, unless I am 150% sure my dates are correct.
