Write a story for a book. Stories for books usually takea while to write. You can never tell how long. Some stories seem to fly right out your pencil. Some stories are like turtles. It changes with each story.
Enjoy your writing! Write until you get tired. Then put your story in a safe place until the next day. You can start it again after your brain has thought about it overnight.
Here's a tip--Reread your story every time you start to write on it. Look for things that don't make sense and spelling problems that mix you up. Fix those problems. Don't erase or it will take forever. Draw arrows when you need to change something around.