A television show that airs at 9 p.m. Eastern will be on at the exact same time in the Central time zone if it's 9/8c.
However, it will be on three hours later if it's shown at 9 p.m. in California.
I can watch a favorite show and spend time on the phone with somoene in Chicago as we watch it together. I can call my friend in California and tell her exactly what will happen three hours before she will see it.