How quickly can sherry notes show up in an oxidized beer???

So, I entered a chocolate stout in a local homebrew competition last week. The wife just reminded me that I tasted my entry (a chocolate stout) with a friend on the same day that I dropped said entry off, and it was a very nice, chocolatey stout - not a sweet chocolate, mind you, but more of a bitter baker's chocolate kind of thing.

Anyway, that was last Sunday. The competition was last Thursday night, and the beer scored pretty low (I think it averaged a 22). The judges both told me they couldn't pick up any chocolate, which absolutely puzzled me. I figured it must've been a case of palette fatigue or something, then I saw the score sheets both cited oxidation, which I thought was way off base.

So, I took another taste the following morning and, sure enough, got a nose full of sherry in the aroma, and the sherry flavor completely masked any chocolate flavor in the beer.

Now, after going through my notes and comparing this beer to my buddy's half of the batch, which shows no similar signs of oxidation, I'm pretty sure I know where I picked up the oxidation (during transfer to secondary to age on cacoa nibs, which he did not do with his half), so I think I have a handle on that part of the question.

But is it normal for sherry notes like that to show up in 4 days' time? I thought that level of oxidation took significant amounts of time to crop up... Now, this particular beer was brewed on St Patty's day, and it's been in the keg and on tap since late April now, so there is some amount of age on it. But I would've expected to note a hint of oxidation to creep in over time, rather than for it to hit all at once like this. Just curious if this is typical, I guess.

At the very least, I'm glad that we finished off the lion's share of the keg before this cropped up!

Everything I've ever read says that even a batch that is super oxidized will not begin to display the off flavors associated with oxidation for a good 3-4 weeks.

I oxidized the heck out of the beer I'm currently drinking. I don't think it would be possible to introduce more oxygen with an auto siphon transfer. I fully expected the beer to taste like cardboard or sherry, but nothing seems "off" to me and it has been in bottles for about a month and a half.

An interesting story... Thanks for sharing.
I've been trying to understand oxidation with regard to the taste of Hobgoblin beer.
(See the Can you brew it Hobgoblin thread for details.)

Now if I could confirm a oxidation taste to Hobgoblin.

Is there an easy way for your average homebrewer to intentionally produce off flavors in small samples of beer? I'd like to taste what I know is an off flavor for a point of reference.

How did you submit the entry to the comp ? Did you counter pressure bottle or did you bottle and prime the entries when you kegged the rest of the beer? If you bottled when you kegged then submitted later it could have been the bottling process. If you bottled from the keg you could have picked up oxidation there. If you fed them right off the tap it may have gradually crept in and you may not notice. I get a lot of insight on flavor of my beers by people that are not familiar with them. I can't because I drink them across the whole spectrum of life and flavor. Maybe the judges picked up something that appeared late and you slowly got introduced to.

I bottled the entries off of the keg, using Biermuncher's little device (do a search for we don't need no stinking beergun, and that should find it) - pretty dang close to a counter pressure fill.

And, if my OP didn't make it clear enough: those sherry notes were evident in the entries and off of the tap - but oddly, not consistently off of the tap. Some pulls off of the tap, the sherry was overpowering enough to hide all the chocolate character. Other pulls, I (and others tasting it) couldn't pick up any perceivable sherry notes at all. Just freakin bizarre. Granted, this beer was in the keg, all told, probably 3 or 4 months before kicking (that's what happens, I guess, when you brew a chocolate stout for summertime!).