Hi @Abhishek_24,
Looking back through old posts, I believe this is a current limitation with the forecasting tool in QuickSight. While dealing with the forecasting in a different visual type, the logic works the same in this scenario I believe as it does not allow you to customize the time period; it would have to be based on your current granularity that’s set and does not allow you to pick the window within your granularity that you’d like to forecast.
I’ll mark this as a feature request to promote visibility to the AWS support team.