I have a couple of thoughts.
First off, you claim that
I was wholly unaware at this point that I was doing everything prematurely.
In my opinion, four days in primary, plus a week in secondary is more than enough time for an American Wheat beer. My own go from kettle to glass in ten days, and they really hit their peak after two weeks. So I don't think that time is what's causing your taste problem.
That said, I also think that spending a LITTLE more time in secondary with the cherries isn't a bad idea. You'll pick up some more cherry flavor, give the yeast more time to clean up phenols and esters, and you'll generally make a better beer. (My own wheats don't get fruit additions, so my timeline is more compressed than yours could be.)
I think that the real problem you're having is that you're expecting the fruit to add cherry sweetness
to your beer in addition to cherry flavor. It won't.
Unless you filter or pasteurize first, adding fruit to a beer won't make the beer taste precisely like that fruit: all the fructose - the sugar that makes fruit sweet - is consumed by the yeast and turned into alcohol and CO2, leaving flavors that a lot of people (apparently you included) perceive as sour. My suspicion is that that's what's happening. If you want a sweeter beer, you have a couple of options:
Filter/Pasteurize: One option is to filter or pasteurize your beer before you add the fruit. That removes the live yeast, so all the fruit flavors remain in the finished beer. From your question, it sounds like this is a technique that you should maybe wait on, but be aware that it's an option that's out there.Sanitation:
Lactose: Beer yeast, for the most part, can't consume lactose, which is why that sugar will remain in your wort and lend sweetness. You can sweeten your cherry wheat by pouring a measured glass, and then tasting the beer with measured doses of lactose; keep adding the sugar until it tastes the way you want it to. Once you've decided on the ratio that works for you, you can add the lactose to the finished beer along with the priming sugar. Presto-bango you have a sweet cherry wheat!
One caution with using lactose, though: it's the same sugar that's in milk, so if either the bride or groom is lactose intolerant, they will not thank you for adding it.
You claim that . . .
I know that my sanitation techniques are not the issue
. . . but we have to talk about that anyway. Most people find vinegar tastes after their beer is innoculated by acetobacter, a bacteria that brewers sometimes use in sour beers. It can also add an unpleasant vinegar flavor to regular beers when acetobacter sneaks in.
Cleaning: I assume, from your confidence, that you did a good job sanitizing your primary fermenter, your tubing, siphons, all your equipment, the air-lock, etc. Did you remember to clean them, though? Proper sanitation is a two step process: first you clean with a chemical cleaner like PBW or Oxyclean, (rinse), and then you sanitize with a no-rinse sanitizer like iodophor or star-san. If you don't clean before you sanitize, you're leaving big colonies of bacteria that your sanitizer can't handle.Yeast:
Cherries: Next, Did you remember to sanitize the cherries? Canned purees are usually pasteurized, so sanitizing them sometimes seems like overkill. . . but if you're even worried about getting an acetobacter infection, then you should definitely sanitize the cherries. Also, did you dump the cherries straight from the can into the secondary fermenter? If so, did you remember to sanitize the OUTSIDE of the can? The cherries can pick up an infection from there while being poured.
Scratches: Next take a look at all of your plastics: tubing, fermenters, bottling wand, etc. Do you see any scratches? If there are scratches in the plastic, the bacteria can sneak in there and avoid both the cleaning solution and the sanitizing fluid. The only good way to deal with scratches is to throw out the piece altogether and replace it. (Or repurpose it for sour-beers.)
Have you successfully brewed this beer without
adding cherries? If not, consider whether the yeast you're using is appropriate for this style. A lot of people use a neutral yeast for American wheats like US-05, WLP001, or Wyeast 1056. I use a Kolsch yeast that has been going in-house for about a dozen generations, and I think it adds an almost
sour complexity to the fermentation that I really like. If this isn't an American wheat, though, then none of those yeasts would be appropriate.
What strain are you using, and at what pitching rate? Depending on the yeast you're using, you could be getting off-flavors from under-pitching.
I hope this gives you a good place to start. Wheats are tricky beers to get just right, and diving right in with a secondary fruit addition is daring. I think that you can get it right: just be patient, pay attention to sanitiation and yeast, and it'll turn out great.