i'm fairly sure it is something to do with timezones.
The US is spread across 4 time zones (eastern, central, mountain and pacific), ie if its 7pm in New York(eastern) then its 4pm in LA(pacific).
So 9/8 would mean 9 O'clock eastern/ 8 O'clock central or whatever zones the tv show was being broadcast in.
In North America, television networks feed their prime time programming in two blocks: one for the Eastern, Central, and Mountain time zones, and one for the Pacific, Alaskan, and Hawaiian time zones to their local affiliates.
The time zone that relates to Greenwich Meantime is generically called Central Time (CT). The central zone is one hour ahead of the Mountain Time Zone and one hour behind the Eastern Time Zone.