There is build in profiler that shows that time: Sheet Properties->Objects->Time.
But there are some notes. As the calculation engine is multithreaded when there are more than one object these values are useless 'cause you don't know when one object starts and other ends. And there is no total time.
Also QlikView caches the result of calculations and you see zeros (even if you reopen the document).
So first you have to place the object to optimize on the separate sheet. Restart QV and check the Time for the object.
Then optimize it, restart and compare the results.
Then as the calculation is multithreaded you can repeat it for the entire sheet and see the result. Unfortunately for this case you don't have any metrics only your eyes.
The server makes calculations a little bit different (cause QV uses different in-memory structure depending on the size of free memory), so you can try and check the result of an optimization there but there is also no access to the metrics.