I usually create two datasets:

1. StartDate

SELECT CAST((CONVERT(varchar(10), GETDATE()-9, 101)) AS DATETIME) AS StartDate

2. EndDate

SELECT CAST((CONVERT(varchar(10), GETDATE()-2, 101) + ' 23:59:59') AS DATETIME) AS EndDate

Then set the parameters @StartDate and @EndDate equal to the values of these two datasets.