Apple - Disable iPhone timed auto lock when an app is running?

It is not possible to disable Auto-Lock for specific apps through iOS settings. A workaround is to manually disable Auto-Lock in settings, run the app, and then enable it again once you're done.

An app can request iOS to disable Auto-Lock. In this case, you should contact the Citymapper developer for an update to allow this.

Engage Google Maps turn-by-turn directions. Turn on your app with directions running in the background. Phone will stay on and lit indefinitely. Close both apps when done.