[piQ]

"Events scheduled within three days of today's date cannot be booked online. However, Information Sessions and Campus Tours listed for this date are still available. We encourage you to attend on a walk-in basis."

Basically I was one day late I was planning to visit on Monday but now I can't register a campus tour online. Does the walk-in basis mean I can go on the campus tour without scheduling my visit online?

[astar]

Yes, that is exactly what it means.
Basically, from my experience, they usually need that time to get all the confirmation stuff sent to you and get it all organized for you.

It means you cannot reserve a spot, but there is room for you to go and visit.