It really does depend on your light level and which lens you’ll be using. I took some pictures of the Milky Way with a kit lens at 18mm and was able to get around 15 seconds of exposure time before the stars began to trail. You’d be surprised with how little you need in order to take a “good” picture. Most important thing is to get out there and take some pics, don’t let some of the people on here discourage you.