They usually base it off of your contractions though. They advise to come in when you reach active labor, which is when your contractions are 5 minutes apart. If they aren't, and you're still in early stages of labor, theyll most likely send you home. Hope this helps! I took a class at my hospital taught by nurses and labor&delivery experts so that's how I know. Goodluck! :)
You get admitted if you are 4cm or more. They might stop your labor if you are before 37 weeks too.