There is only a JIT horizon field, not a forecast horizon field.
You can maintain valid from and valid to dates on both Forecast and JIT, and they can be different ranges.
Let's assume you set up an SD scheduling agreement using transaction VA31 and document type LZ and entered a line item by putting in an SAP Material and the Customer Material Number.
Goto > Item > Forecast Delivery Schedule or the button at the bottom of the Overview screen gets you to the Forecast Delivery Schedule. Here you enter the Forecast dates and quantities provided by the customer. You only need to put in a Delivery Schedule number, usually a release number, and the release date in the Delivery Schedule date field.
On the forecast side, that's all you need. The horizon is basically the date of the last delivery schedule line. The header data is stored in VBLB and the delivery schedules in VBEP.
If you also have JIT delivery schedules to manage, it's basically the same, except Goto > Item > JIT Delivery Schedule. The one additional field is the "JIT Horizon" date field. If you are using MRP for DS Type = 'B' or 'D' the date you put in the JIT Horizon is the ending date of JIT schedule lines.
This JIT Horizon date is important, because it determines where to stop getting the schedule quantities from the JIT Delivery schedule, and where to start getting the schedule quantities from the Forecast, so we don't double up of requirements on the delivery due list and MD04.
The JIT Horizon date comes from E1EDP10-ABHOR if the customer EDI comes in and updates the scheduling agreement via Idoc.
When mapping, if the customer doesn't provide an accurate JIT horizon, you may need to use the last delivery schedule date.
You can populate the ABHOR field in the Forecast Idocs too. But it doesn't matter for SAP processing.
For the Valid From and Valid To dates, these are mapped into the E1EDP10-ABRAB and E1EDp10-ABRBI respectively. On VA32, you need to be in the Forecast or JIT delivery schedule tab, and then click the Delivery Schedule Header button and then the Inbox tab.
If looking at VBLB and VBEP, remember the Forecasts are ABART = '1' and the JITs are ABART = '2'.
