Not an ARM calculation, but an old-school approach that works on any processor: at the beginning of your interrupt function, pulse a output pin high then low.
Hook up a logic analyzer to the interrupt line and the output line you are pulsing and measure it. If you can capture a lot of results and have abilty to dump timings as text to a file, then examine all to calculate the min, max, avg. This will be helpful to determine jitter.
You should be able to look at the interrupt source code, if in C, then subtract the instruction timing from where your instruction pulses the line to the beginning of the interrupt code from the above time measurements to come up with the answer.
People want nice pretty answers from a book...but it is hard to beat real-world measurements.