Guidelines regarding when to sleep?

Hello, I am a Christian trying to study a little bit more about how Jewish scripture teaches Jewish people to live. I have become curious about Shabbat because I am interested in learning how to better practice observing the sabbath. I do have a few questions. So, is sundown to sundown considered what Americans call the sunset as in around 5:30 pm or is it later after it starts to get a little bit darker out? I also want to ask whether there are any laws regarding when Jews go to bed. Do they go to bed shortly after sundown since the new day has begun or do they start the next day for a few hours before sleeping?

Thanks for anybody who took the time to read and answer.