try something like this
SELECT Count(Date_Sent) AS TotalQueries,
SUBSTRING(CONVERT(VARCHAR(11), Date_Sent, 113), 4, 8) AS Month,
RIGHT(CONVERT(VARCHAR(7), Date_Sent, 120), 2) AS Month_Order ,
SUM(CASE WHEN DATEDIFF(HOUR, FirstResponse, LastResponse) < 2 THEN 1 ELSE 0 END) AS LessThan2Hours,
SUM(CASE WHEN DATEDIFF(HOUR, FirstResponse, LastResponse) between 2 AND 24 THEN 1 ELSE 0 END) AS LessThan24Hours,
SUM(CASE WHEN DATEDIFF(HOUR, FirstResponse, LastResponse) between 25 AND 48 THEN 1 ELSE 0 END) AS LessThan24Hours,
SUM(CASE WHEN DATEDIFF(HOUR, FirstResponse, LastResponse) between 25 AND 48 THEN 1 ELSE 0 END) AS LessThan48Hours,
SUM(CASE WHEN DATEDIFF(HOUR, FirstResponse, LastResponse) between 49 AND 72 THEN 1 ELSE 0 END) AS LessThan72Hours,
SUM(CASE WHEN DATEDIFF(HOUR, FirstResponse, LastResponse) between 73 AND 96 THEN 1 ELSE 0 END) AS LessThan96Hours
FROM AskAO.dbo.AskAO_Stats
WHERE Date_Sent BETWEEN '6/1/2012' AND '6/30/2013' AND FirstResponse != '' AND LastResponse != '' AND FirstResponse < LastResponse
GROUP BY SUBSTRING(CONVERT(VARCHAR(11), Date_Sent, 113), 4, 8), CONVERT(VARCHAR(7), Date_Sent, 120)
ORDER BY SUBSTRING(CONVERT(VARCHAR(11), Date_Sent, 113), 4, 8)