it will appear within a given window of time anywhere within the next hour, but no sooner than 15 mins from your post if i remember correctly
so there is no way to tell for sure that your stuff is on the market given that someone else could have posted the same number at the same price as you
but your important events will let you know who bought your stuff, and how much, off of your market post
so, you can only tell for sure that your items WERE on the market