It is important to visit colleges in which you have the greatest interest. The spring of your junior year is a good time to visit colleges.
Most colleges offer tours and interviews in the summer and fall.
When you visit, make sure that you are prepared. Call before you visit to find out the schedule for tours and interviews. Most tours and interviews take an hour each. You should allow about three hours for a campus visit. An ideal visit would include a tour, an interview and then free time.