Depends on size, your's being 12' wide by 24' long, half an inch is well inside the limit for both directions, most say within an inch, visually, you probably want it to be somewhat less, 1/8" is great, i doubt anybody could get any more accurate. If everything is compacted the same all around, then your settling should happen pretty even, this means the whole pool will sink that settling amount, not just one end, so essentially, your whole pool may just sit 1/4 inch lower than when you first put it up.