depends on what type of fluid you are using Type 1, 2, 4, mix ratio 50/50, 75/25 or 100% and the manufacturer and ia it hot oe cold.
We have been using 75/25 hot type 2 Kilfrost ABC-K plus and the hold over times in snow at -1C is something like 1hr 25 mins. Many years ago with older type fluids you were wasting your time in snow but nowadays they have improved immensely.
Much would depend on if the wings were cold soaked or not, frosty before it snowed or not, or if it was just a light coating of snow, so to say 320 lts is not enough is completely unfounded.
I was responsible for the removing/deicing of a 744 last week in the snow and we used anything from 500-800 ltrs, no 2 a/c are the same. So could you do an A330 with 320 lts of course you could. Could you use 800 lts on an A320 you could but I would suggest unless there was 4 foot of snow on an extremely cold soaked wing I would say that was excessive and would be questioning the operator, after all I am the one signing the a/c out as fit to fly not the rig operator.