Calculate the time difference between of two rows

To achieve what you are asking try the following (UPDATE after edit from OP):

SELECT A.requestid, A.starttime, (B.starttime - A.starttime) AS timedifference
FROM MyTable A INNER JOIN MyTable B ON B.requestid = (A.requestid + 1)
ORDER BY A.requestid ASC

IF requestid is not consecutive then you can use

SELECT A.requestid, A.starttime, (B.starttime - A.starttime) AS timedifference
FROM MyTable A CROSS JOIN MyTable B
WHERE B.requestid IN (SELECT MIN (C.requestid) FROM MyTable C WHERE C.requestid > A.requestid)
ORDER BY A.requestid ASC

The accepted answer is correct but gives the difference of numbers. As an example if I have the following 2 timestamps:

2014-06-09 09:48:15
2014-06-09 09:50:11

The difference is given as 196. This is simply 5011 - 4815. In order to get the time difference, you may modify the script as follows:

SELECT A.requestid, A.starttime, TIMESTAMPDIFF(MINUTE,A.starttime,B.starttime) AS timedifference 
FROM MyTable A INNER JOIN MyTable B ON B.requestid = (A.requestid + 1) 
ORDER BY A.requestid ASC