Acetaldehyde and oxidation are different. You can prevent Acetaldehyde by good sanitation practices. Oxidation may be prevented by avoiding hot side aeration, and keeping O2 out of your beer after fementation. Splashing has been know to cause aeration.
It took about two weeks to develop. I know that acet can form from bad sanitation, but I don't think this is it. I had have of the batch in a party pig and it was great for two weeks and only when it was almost gone did a little sourness appear. I read that oxygen at bottling can cause a reverse reaction of alcohol to acetaldehyde. I believe I let in too much O2 from my siphoning hose. I use brown bottles. It isn't skunk. It has a budweiseresque bite. It is still drinkable but I wondered if anyone else had this happen.