Most colleges and universities are open year-round for visits and campus tours. But the time of year you visit will impact what you see.
Use your network and technology. Just because you can't visit doesn't mean one of your friends or family haven't. Maybe they know someone who has been to campus and can share their thoughts with you.
The campus visit is the most important action you can take to determine whether a college is a good fit for you. You should spend four years there, so it is worth investing some shoe leather, rubber, or plastic in checking it out!