Calculating the launch time of apps

I would like to compare the launch time of a few apps On the app store. Obviously I do not have access to source code, so I was wondering what is the best way to get accurate results ?

Is there a way to know when the system makes a 开发者_StackOverflow中文版call to applicationDidFinishLaunching (without source).

Any help is appreciated

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Video them starting up and look at the time codes.

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Maybe fire up Instruments and look for some kind of timeline evidence with one of their profilers?