SELECT CONVERT(varchar(10),OrderDate,101) AS [DAY]
	 , DATEPART(hh,OrderDate) AS [HOUR]
	 , COUNT(*) AS [OrdersPerHour]
  FROM #Orders
GROUP BY CONVERT(varchar(10),OrderDate,101)
	 , DATEPART(hh,OrderDate)
ORDER BY 1,2

/* Table to hold values...this would be a real table... */
Create Table #DimTime(TimeId int identity, FromDate DateTime, ToDate DateTime)
/*
Insert actual date type values for FromDate and ToDate 
for every date that is a saturday (for a few years back and forwards)
Example:
*/

--insert initial saturday record for 2009
Insert #DimTime(FromDate, ToDate) Values ('2009-07-04 00:00:00', '2009-07-04 00:9:59')

--hold MaxFromDate
Declare @MaxFromDate DateTime

--initialize variable
Select @MaxFromDate = Max(FromDate) 
From #DimTime

--populate table
While @MaxFromDate < '2009-10-01' 
Begin
	If DatePart(hour,@MaxFromDate) = 23 and DatePart(minute,@MaxFromDate) = 50
	Begin
		Set @MaxFromDate = DateAdd(day,6,@MaxFromDate)
		
		Insert #DimTime(FromDate, ToDate)
		Select DateAdd(minute,10,@MaxFromDate), DateAdd(second,59,DateAdd(minute,19,@MaxFromDate))
	End
	
	Insert Into #DimTime(FromDate, ToDate)
	Select Max(DateAdd(minute,10,FromDate)), Max(DateAdd(minute,10,ToDate)) 
	From #DimTime

	Select @MaxFromDate = Max(FromDate) From #DimTime
End
--------------------------------
--now your query would be this (or something like it)
SELECT t.FromDate, t.ToDate, Count(o.Order_Id) OrderCount
FROM #DimTime t
	left join #Orders o on o.OrderDate between t.FromDate and t.ToDate
GROUP BY t.FromDate, t.ToDate
ORDER BY 1
--------------------------------
Drop Table #DimTime