My son was in the NICU for 20 weeks total but he recovered within a week or so from his duodenal atresia surgery. They actually didn't see his right away so his surgery was about a month after he was born. He was born full term and went into a different surgery the day after he was born. I would think that as long as your son is doing well they will do surgery quickly after he is delivered.
Have you talked with your OB about him going to the NICU? I'm assuming he will have to go and if he does you might be able to go visit before you deliver so that you will be a little more comfortable once he is born.
Also, my best advice is to stop looking on the Internet. I know it's hard to do but is will cause more stress than anything else. Anyone can write anything on the Internet so what you read may not always be accurate (I'm sure you know that already) but as a mom looking for information you are going to be more trusting of everything you read. All the negative info you read is just going to send you into a panic these last few weeks of pregnancy when you really just need to try to relax as much as possible.
Also, I'm not sure if you are planning on *** feeding. If you are you should ask for a pump as soon as possible. Your son will not be able to nurse when he is born. The duodenal atresia will prevent him from being able to digest food and the medical staff won't let him. The sooner to giving birth you start pumping the better. You can store what you get with the date and then new he is able to start eating you will learn to nurse him and be able to give him the pumped milk you produced in the beginning. If you are planning to formula feed, just disregard this whole paragraph!
Please ask me any questions you have. I remember looking for any "veteran" NICU parents to help guide me through those first few days. Good luck!