I have brought several in at an older age. Each one took a different amount of time to adjust completely. I think they adjust for the most part fairly quickly, with a few things that need work. Midnite, my male GSD took about 3-4 months to completely adjust. He has turned into a wonderful dog. Really all of them have. They are a commitment and once I take them in they aren't going anywhere. I don't feel they are disposable and I understand that by moving them from home to home can be even worse, so they stay put with me.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD