It's obviously impossible to play these chords on the beat.....
I usually play the chords right on the beat and the octaves just before.
Speaking of which, I actually play the preceding octaves as full 4-note C# minor chords in each hand in bar 53. Somehow, after memorizing it some years ago, that crept in after I hadn't played it for a few months, because that is the climax of the whole sequence and therefore, the loudest chord, and somehow I thought Rach wrote two full chords. By the time I discovered my error, I'd already performed it twice that way, and felt it sounded a little thin when I played it as written, so I've stayed with my 'improvement' ever since.....
So, I am trying a different practice technique where I prepare my hands in mid-air while moving in an arc and land on the chords immediately without preparing first. Obviously, I'm practicing it slowly but because it's only one movement instead of two I believe it will help me play this chord the way it should. I made some improvement already but I'm still hitting wrong notes at the moment.
Any thoughts? How would you practice this?
Can you land precisely on those chords from 'nothing'? That is, you know the keys you want to play in each hand, and you just play them immediately without any preparation, out of thin air as it were, without any preceding notes to 'guide' you, or to launch your hands from.
I think that is the sort of 'position sense' you want to develop with your hands and fingers, to tackle stuff like this. Almost instantly, you can form the shapes with your fingers that you need to land precisely on those notes in the chords, with all of them sounding together and properly voiced. And you are able to do that from a short distance above the keyboard.
What you could do is to get used to playing the chords by themselves: maybe play them several times (perhaps with different voicings each time) until they feel very familiar and natural, and the positions of your spread hands and outstretched fingers feel totally normal. Play those chords at the start of every practise session, and at the end, as many times as you feel like playing, until you can just sit down at the piano and immediately play them without any preparation.