VT website:

All university community members must display a permit or pay the daily charge to park on campus, from 7 a.m. to 10 p.m., Monday through Friday (unless otherwise noted by a sign). Visitors (non-students or non-faculty/staff) may park in any faculty, staff, visitor, or student parking space if they have a valid visitor parking permit and if the space is not restricted by signs. Some restricted areas include ADA spaces, carpool spaces, loading zones, service vehicle zones, timed areas, sidewalks, grass, admission areas, the Hahn Hurst Basketball Practice Facility Lot, the Basketball extension lot, Pamplin Lot, Owens Lot, and Dietrick Dining Hall Lots. Visitors are recommended to use the F/S section of Perry Street Lot, Litton-Reaves Lot, Coliseum Lot, Derring Lot, Perry Street Parking Garage, Washington Street, Litton-Reaves Extension Lot, and the North End Center Garage (payment required 24/7).
You can buy a pass at Parking Services (across from Tennis Center), or use the app (ParkMobile). You can find the app online (iOS or Android), tie it to a payment method, and you're all set. You'll see signs for parking zones near parking spaces to identify where you're parking. Charge is $6/day.
Additionally, the condition described by @RJHokie is a constant state for parking services. Note the listed times when permits are needed.