Generally speaking we do not get patch notes before the patch for the ‘small’ patches. This is due to the fact that the maintenance time will be the same across all servers and if the notes are released beforehand, the players whose timezones allows them to both read the notes and be online before the servers go down, can take advantage of any effects it will have on the market ward (take for example the relic weapon quest and the effect it had on materia). And even when they do release preliminary patch notes, the sections on items and recipes tend to be left out so as not to give anyone an advantage

By only releasing the patch notes after the maintenance has started allows everyone to be able to read it and fully absorb the implications so everyone can start out at the same level when the servers come up.

Patch 2.55 will be heavily story-based as they wrap up the 2.0 storyline, so most of the patch notes will probably revolve around the quests with some information on the MGP balances for the Gold Saucer. It really doesn't seem like things that you desperately need to know before the servers go down, and will likely contain some spoilers, so I don’t really see a problem with waiting for them.

As for when they will be available – the maintenance is 6 hours, so I reckon about halfway into it the notes will come. Until then, just sit tight and be patient