If you're one of these writers, let me give you a word of advice. First of all, don't concern yourself about submission guidelines, story length, chapter length, precise genre typing of your story and all the other technical stuff. Especially if you haven't even started writing your story. Until your story is finished, these questions, and other related topics, are basically irrelevant. Just write your story.
Stories take on a life of their own and create their own length and flow.
After writing, edit without mercy. Make each word count. Be sure your scenes and characters are clear, alive and interesting. Include at least one conflict, and have that conflict resolved by the end of the story. When your story is done, that's when you research markets and follow their guidelines.