How can I lengthen the time before a passcode is required on iPhone?

You can change this here:

Settings → Face ID & Passcode → Require Passcode

Please note that the time before your iPhone asks for the Passcode can only change if Face ID is not set up. With Face ID set up, you can only choose Immediately.

kathleenfromoh wrote:

Thank you for letting me know that it's now impossible to change the idle time. I wish I'd been told that before the person helping me set up the new iPhone helped me set up facial id. The setting of "immediately" is annoying. Apple, are you listening?

No, Apple is NOT listening. This is a user-to-user forum. If you want to set a longer time you can disable FaceID. But there is also a screen idle setting in Settings/Display & Brightness/Auto-lock. This is how long the phone will stay unlocked if you don’t lock it manually. The Require Passcode applies when you manually lock the screen or the Auto-lock times out.

See the section about setting up a passcode in this support article --> Use a passcode with your iPhone, iPad, or iPod touch - Apple Support

and the part about Require Passcode

Apple, are you listening?

Not here. This is a user to user site.....we are all users.....just like you.

If you want to provide feedback to Apple, you can do so here:

Feedback - iPhone - Apple