I wonder if placing TWOK in 2285 has something to do with the Romulan Ale McCoy gave Kirk, which was a 2283 vintage. Could Okuda wanted to place it sometime after that?
I've never figured out whether "It takes this stuff a while to ferment" was meant to be literal or a joke. It always felt to me like the latter, like the implication was that it was very young, low-quality hooch and McCoy was being sarcastic. How long does fermenting ale normally take?
Though to be completely fair there was no Memory Alpha back then to check this stuff and we weren't firmly settled yet on the timeline of the original series (I think it was settled to the late 2260s by then, just not exact years yet since Q2 was still years from airing).
As I mentioned, the Chrono just adopted the already long-standing fan theory that TOS took place exactly 300 years after it aired. That goes back to Geoffrey Mandel's fan reference books published in the '70s and '80s. Before TNG: "The Neutral Zone" locked in an exact calendar date for the first time, there were two competing theories in fandom of when TOS took place. The other was the scheme featured in the
Spaceflight Chronology, which put TOS in the first decade of the 2200s -- a compromise between the "200 years" lines in "Tomorrow is Yesterday" and "Space Seed" and the "23rd century" references in
The Making of Star Trek, the Blish adaptations, and the movies. That would've put TWOK in the early 2220s sometime, but the Romulan ale's "2283" could've been a stardate or a Romulan calendar date.
But "The Neutral Zone" put TNG season 1 in 2364, and we knew it was supposed to be 78 years after the TOS movie era, also that McCoy was 137 in that year. So that conclusively ruled out the SFC scheme and narrowed TOS down to around the 2260s. (I was using the SFC scheme in my personal chronology, so as soon as "The Neutral Zone" aired, I had to redo the whole thing, in pencil and paper.)
Hmm, maybe that's the reason for the Okudas' movie dates. The most recent movie when "The Neutral Zone" came out was TVH, and 2364 - 78 = 2286. Although the 78-year thing was never spoken onscreen (until GEN, which was 78 years after the
Enterprise-B prologue), so it's not like it was canonically binding. It would be weird if that were the reason.