The juice is super sweet, and I imagine that it presents a high amount of fermentables to the overall mead. I debated the same situation, however - do I just follow the recipe as stated, or do I let it get going and then add in the liquid + cherries ... or do I finangle a different way of doing it?
That said, I debated doing a 5 gallon batch of this ... and decided to do 2 one gallon batches. I did one with the local supermarket preservative laden cherries, and I did one with some high end "organic" cherries. I never thought I would buy anything organic unless it was cheaper ... but this is homebrew, by golly - time to get maraschino cherries shipped to my door!
I used Tillen Farms cherries
http://www.worldpantry.com/cgi-bin/ncommerce3/ProductDisplay?prmenbr=207315&prrfnbr=2776937 for my test batch. Seemed the best bang for the buck. I must say that the flavor of these cherries is so far above and beyond the local store bought variety. Oh my goodness, there were layers in the flavor of these cherries, as opposed to a simple "meh" that came from the store bought brand. If I ate them on ice cream regularly, or used them in really any other capacity, I might be a changed man. They really are that good.
I did everything the same, prep work, yeast, etc. The only difference is that, treating the preservative laden liquid like the lemon juice for skeeter pee ... I let the liquid itself sit (in the fridge with a towel over it) for a couple days. I hoped that this might encourage a bit of a release of the preservatives.
As of right now, I have no idea how these are coming along. The reason is because the batch that I started first, with the local store bought variety, finished fermenting much more rapidly than the Tillen Farm's all natural variety ... and it's only about 6 weeks old on average. (7 for the store bought, 5 for the organic style). Judging by the fact that it has cocoa powder in it, and the aging will require ~1 year ... I can give you feedback in another 46 weeks if you'd like. However - both are completely dry (or bordering on such).
I'm also debating using some excess preserve-filled cherry liquid that I have left from when I used the cherries to make jello shots to use as a back sweetener. I'm holding on to it - and figure it will kill 2 birds with one stone. Sorbate my mead as well as backsweeten all at once!
Also of note ... I had to clean my vaulted ceilings when I put a stopper/airlock on this. I kid you not, this went ~15 feet horizontally, and ~15 feet vertically before hitting the wall. Honey + chocolate = harder than heck to clean off walls. And ceilings. And floors. And kitchen cabinets. Etc. Start this in an ale pail ... or use a blow off tube ... or something ...
(Updated link for cherries)