This is from the Zentrum site:
Hours of Operation
The Zentrum Museum
Open Monday - Friday from 9:30 a.m. to 5:30 p.m.
For information call 1-864-989-6000.
Entrance to the Zentrum is free.
Guided Factory Tours
Tours will be suspended effective June 1, 2007 as the plant prepares for new model production.
Holiday Closings
4/6 Good Friday
5/28 Memorial Day
7/4 Independance Day
9/3 Labor Day
11/22 Thanksgiving
12/24 - 1/2 Holiday Shutdown
Event Schedule
8/3 - 9/2 Roadster Homecoming
9/29 Red Cross Bike Rally
10/19 - 10/21 EURO Auto Festival
11/2 - 11/4 Hilton Head Concours d'Elegance (not on-site)
http://www.bmwzentrum.com/information/tour_times.asp