We can define the project schedule date range by using “ScheduleStartDate” and “ScheduleEndDate” API properties.
please find the code snippet below.
<ej-gantt id="ganttSample" datasource="ViewBag.datasource"
Please refer following ASP.NET core sample link with schedule date range.
Is this your requirement if not please revert us with your exact requirement, it will helpful to serve you better.