The planned hours in the TKS are only calculated until Schedule Horizon is activated. After that, PMI is using SMART hours.
Horizon days are used beyond the period you have scheduled in TKS. If you are usually making schedules for 10 days ahead, the horizon should be set to 10 days. After this PMI is suggesting a schedule based on your forecasted productivity target and live forecasted cost driver (output).
Your schedule is visible between the red line (today) and the green line (Schedule Horizon), after which there is a SMART schedule.
If you have a schedule that goes longer than the Schedule horizon, you can click on the schedule to see this in the graph or extend the horizon days.