Here you can enter the order's start period and leave the finish period field empty. When a manufacturing order has been registered, a finish period will be calculated for the order based on the parameters that apply for the loading. The determining factors are, among others, the queue times for work centers, setup and unit times for the operation, and the production calendar.
Conversely, you can perform "back planning" by leaving the start period field empty and instead enter a finish period. If the Start period appears in red, then the start period for the order has been entered in past time.