There are a number of reasons why the time frame may be so close.

First, the issue in this case was a relatively simple one; all the judge needed to determine was whether the search conducted by DoD of their records was sufficient. Honestly, the law was against CAUS on this one, and the issue was rather cut and dry. It therefore did not require a lot of research by the judge to come to his conclusion; he may have just taken much of his opinion wholesale from the DoD's brief.

Second, the appeal was heard by only one judge, which makes for a quick decision when you don't have a large number of judges on the case. The appeal was not heard en banc, meaning with the full panel of judges (there are 25 or so on the Ninth Circuit), which would have delayed a final judgment for possibly many months. And it is possible that the District Court's ruling, which was released in January, was very close to the beginning of the term for the Appeals Court, which allowed it to get on the docket unusually quickly.

If you're interested, the citation is 21 Fed.Appx. 774. "Fed.Appx." means that it's in the Federal Appendix, which is essentially a blackhole of Federal jurisprudence. As to whether that is significant I will leave to the reader.