[Chloé Richmond]

I came up with this solution, which I found more useful:

let framerate = 1/thisComp.frameDuration;
let targetFrameRate = 12;
let frameOffset = 1; // (offset in frames);
Math.floor(value*targetFrameRate)/targetFrameRate+frameOffset/framerate

There’s also the solution of precomping it and then adding an adjustment layer with posterize time that you can move around, but I found that a bit too cumbersome for my liking.