[If each iOS device] would be unlocked using a 4-digit PIN, the time to bring them into use would be about 2 seconds. Expanding to a 6-digit PIN would probably increase that to perhaps 2.5 seconds (accounting also for failures due to input errors.)
It turns out that, based on the installed base numbers, moving to the more secure 6-digit code would add 2.8 billion hours to the total time to unlock the world’s iPhones and iPads. That’s 321,000 years of waiting added for every year of use.
Fortunately we got Touch ID to replace PIN entry and the time to unlock the iPhone/iPad has decreased to perhaps 1 second, saving 5.6 billion hours of unlock time vs. 4-digit PIN.
Reminds me of an interview with Larry Tesler in Dan Saffer’s Designing for Interaction, where he said the following:
If a million users each waste a minute a day dealing with complexity that an engineer could have eliminated in a week by making the software a little more complex, you are penalizing the user to make the engineer’s job easier.
I guess it’s no coincidence that Larry Tesler was an early Apple employee, back when Steve Jobs argued that decreasing Macintosh boot times would save lives.