I always just sprinkle a bit in and around the planting hole when I transplant the brassicas. Don't know if this makes a difference to chucking it over the ground now or for the winter?
I agree with doing it at the time of planting, I think by doing it earlier the bulk of it may leech away with the winter weather.
As I have explained before I always think when the liming is done after planting it is there to 'coat' the new roots forming on the plant, which I guess helps to prevent the onset of 'club root'
Another reason is; I 'muck' my beds in the autumn and this ensures I don't muck & lime at the same time.
But this is only my way! others may have different reasons for doing what they do, and all I say to that is;
do it the way that suits you