Center of box is the time when the satellite is in the center of the allowed area for the satellite to drift.
You can find out when an Intelsat satellite is going to be in the center of the box by going to this website: Intelsat Satellite Ephemeris Data
Under: "Intelsat Americas Region (°W)"
Then Under: "Center Of Box"
Click: "View"
You can find out when an Intelsat satellite is going to be in the center of the box by going to this website: Intelsat Satellite Ephemeris Data
Under: "Intelsat Americas Region (°W)"
Then Under: "Center Of Box"
Click: "View"