This question is applicable to both iPads and iPhones: how do I extend the lock screen timeout? By that I mean the time from when I see the "slide to unlock" message to when the screen goes black again. Right now when I press a button to wake my device up, I have about four or five seconds to slide the screen to unlock, before it just goes dark again. I would like to extend this timeout if possible. How do I do it?
Without jailbreaking your iPhone there Is no option to change that.
I have accidentally found that pushing the on/off button exactly as the lock screen is dimming will keep the lock screen lit. No idea how long it stays on but doing this does prolong lock screen. It lasts at least 6 minutes and possibly forever. I am on iPhone 7. No idea how to set a timer for it though.
Could not find Auto-Lock, search box took me to Display & Brightness and it's there. You can set to 2, 5, 10,or 15 minutes, or Never.
iOS 8 Settings > General > Auto Lock
For those still searching for a workaround for this, you can also slide the display up or down with your finger to extend the display. That is, after you "wake" the device and see your notifications, put your index finger on the display and slide it up (or down). Each minimal "scroll" of the screen resets the countdown timer back to 5 seconds, I believe.
You can only do it after jail breaking else it's not possible.
Pressing the on/off button as the screen begins to dim is indeed the solution to this "irritation," as first suggested by Wdtony. I just got the iPhone 7 Plus, on which the lock screen dims about two seconds faster than on my iPhone 5, by my "one-one-thousand" reckoning. This also works for the iPhone 5, so presumedly, it also works for the "6" line of iPhones.
iOS settings > general > Battery > low power mode > off
iOS settings > general > Auto lock