(Wind Waker spoilers, in case you haven't finished it yet, in which case you should stop reading right now and go play it)
You know that tombstone that Michael Jelvis danced in front of on Windfall Island? I haven't tried making out the name on it yet (there's some grass in front of it), but, using
this key (from the Japanese manual), it says "821 - 894" at the top. So Wind Waker takes place in at least the year 894 of whatever year system they use over there. How long after 894 it is might depend on who's in that grave -- maybe the founder of Windfall Island Town?
It's mentioned later in the game that the land has been flooded for "hundreds of years." It's not described as "thousands" or "over a thousand", so it's probably 900 or less. So the year system would apparently be based either on the date of the flood itself or of something before the flood (Creation? The Hero of Time?).
Just something interesting that I couldn't find anyone else on the internet talking about (not that I looked super hard).