I think overnight visits are incredibly helpful.
You get to feel what it is like to be a student at the school, see if Rice feels like a good fit for you. You will hang out with your host and their friends, eat at the servery with them, sleep in their college with them, go to classes with him. It’s a taste of what it means to be a Rice student.
The best advice I can give is don’t be nervous, don’t try to “impress” anyone, just relax and be yourself. Don’t be afraid to ask any questions no matter how dumb. Don’t be afraid to talk to anyone, just say you are a prospie and everyone will be friendly with you. Rice students like Rice and they will be happy to talk to you and will want you to like your experience.