Hi Luis,
Thanks for your update.
We have analyzed your query. GanttControl’s StartTime and EndTime values will be in calculated form for the task values automatically. And we add some extra days in StartTime and EndTime of GanttControl based on Microsoft ProjectManagement. As of now we do not have the support to restrict the StartTime and endTime of GanttControl. However we have already logged the feature report for this requirement internally. We will let you know when once this feature is implemented.
Please let us know if you need further assistance.
Thank you,
Jai Ganesh S