Here's a bit of code to get you started:-

SELECT

ID,

TimeStamp,

LAG(TimeStamp,1) OVER (ORDER BY ID DESC),

DATEDIFF(HOUR, TimeStamp, LAG(TimeStamp,1) OVER (ORDER BY ID DESC))

FROM [dbo].[RunningTime]

It uses the LAG function to get the previous value and then uses the DATEDIFF function to compare the two.