date.ToString("yyyy-MM-dd HH:mm:ss.fff")

Shared SomeFunction(ByRef sStartDate as String)
Dim StartTime As DateTime = DateTime.Parse(sStartDate)
command.Connection = connection
command.CommandType = CommandType.StoredProcedure
command.CommandText = "SomeStoredProcedure"
command.Parameters.Add("@StartDateTime", SqlDbType.DateTime)
command.Parameters("@StartDateTime").Value = StartTime.ToString("yyyy-MM-dd HH:mm:ss.fff")