Sure sounds to me like McCoy is being sarcastic, meaning that Romulan Ale ferments almost instantly!
In that case, 2283 could not be a year, because no joke hinging on the passage of small units of time could be based on a datapoint that is given at no better resolution than whole years.
And the joke would still be a really thin one if 2283 were a stardate. Why would Kirk comment (seemingly negatively) on the fact that the beer he got is brand new, or only some days old? Why would McCoy need to respond defensively to that?
It makes much more sense for 2283 to indeed be a year, so Kirk could be worried about the bottle being old and possibly stale, and McCoy could get defensive (because obviously it's difficult to get those things across the border, and McCoy probably dug the bottle out of a dusty cabinet after having acquired it some years ago, instead of somehow managing to procure one from Romulus in a timely manner), citing the slow fermentation issue (whether true or untrue) and knowing his friend would understand.
Incidentally, since we know Romulan ale is supposed to be a potent inebriant, it's probably strong in alcohol and likely to weather a few years of storage rather well...
If 2283 is a year, in any timekeeping system (barring the Scalosian one, perhaps!), then the time intervals our heroes speak about or joke about
must be in the order of years, too.
Time-travel timeline changes is a possibility, but it's a bit of an cheaty fix - I prefer to save that for the really big problems!
It's a nifty fix for the overlapping stardates of "Miri" and "Dagger of the Mind", tho, thanks to "The Naked Time".
Although actually there's no overlap there. Kirk must have misspoken his "Miri" line where the next log entry after SD 2713.6 turns from the sensible SD 2713.7 into the overlapping SD 2717.3. Elsewhere in the episode the corresponding passage of time is indicated in increments of 0.1 units, not in increments as large as 4.
(And I do mean Kirk misspeaking, not Shatner. Perhaps the line was written wrong for Shatner, perhaps Shatner misread it, but it's Kirk who spoke the line in-universe, and we can treat it as an innocent mistake of Kirk's. Using character fallibility does trump using time travel in my opinion, too!)
Incidentally, regarding the Planet of Galactic Peace, I wouldn't put it past the Romulans, Klingons and UFP to have negotiated some sort of a secret peace arrangement prior to "BoT" without deigning to inform Captain James T. Kirk about it. Kirk was spectacularly uninformed about Romulan affairs in that episode anyway!
Timo Saloniemi