I'll do the manual searching labor for the schedule.
Look for standard definition and high definition.
In the San Francisco Bay Area: Comcast 273 and for HD, 757
This link is for Eastern Time (ET in the link)http://channel.nationalgeographic.com/channel/ET/daily/20080123.html
This link is for Pacific Time (PT in the link)http://channel.nationalgeographic.com/channel/PT/daily/20080123.html
Wednesday January 23 6pm PST (3pm EST)
Saturday January 26 7pm and 10pm PST (4pm and 7pm EST)
Monday January 28 10am PST (7am EST)
Wednesday January 30 (schedule currently doesn't show the time)