What does Shepard Smith mean by the "G block?"

Each segment of our shows is titled with a letter of the alphabet. We call the segments "blocks." A block is made up of the time between each commercial break and is sometimes further broken down into smaller segments such as A1, A2, A3...

When Shep Smith refers to the "G Block" he is indicating that it is the seventh and last block of FOX Report. It is usually the segment in which he discusses entertainment and "lighter" stories.

Note from Vern:
In other words the show is nearing it’s end and means “That’s about all Folks”
Sort of like ”That’s about 30 for Tonight Friends”