I submit to a publication and if it hasn't been published by 8pm UK time, I withdraw it, self-publish, and send it to a publication that accepts published stories. I don't know how to tell if it's been scheduled. I've only found out twice because it tells you as you withdraw, but by then, it's too late. You might find this list useful - it's publications that accept self-published stories... https://medium.com/new-writers-welcome/medium-publications-that-accept-self-published-stories-4ca5351e24f6