Reports :: Time Based Graph

I have the following query:

TRANSFORM Count([Copy of qryDailyCountOfValidations].Staff_Number) AS CountOfStaff_Number
SELECT [Copy of qryDailyCountOfValidations].PatternStartDate, [Copy of qryDailyCountOfValidations].[End Time]
FROM [Copy of qryDailyCountOfValidations]
GROUP BY [Copy of qryDailyCountOfValidations].PatternStartDate, [Copy of qryDailyCountOfValidations].[End Time]
PIVOT Format([Start Time],"Short Time");

it shows the number of employees that start a shift at a particular time and the time the shift ends, on any day.What i need to show on a graph is the count number of employees starting at x time and plotting the number of hours the employees are on shift until they leave or another employee starts....

-the y axis is the count of employees
-the x axis is the start time of their shift

10
9
8
7 xxxxxxxx
6 x x
5 x x
4 xxxxxxxx x
3 xxxxxxx x
2 xxxxxxxxxx
1
0
00:00 03:15 05:30.........................23:59

So the above mock up says 3 employees start at 00:00 and continue until 03:15 then another employee starts, then 4 employees continue 06:00, then 3 more employees start, 7 all together, then 5 employees leave later etc...

-the level of detail needed is to plot for every 15 minutes.
-The [end time] is not strictly needed, just included to show what columns i have available

achieving this on a graph on an access 2010 report..i have updated a test database so you can see what the data looks like.