Where to wire in new clock

It's a 24 hour clock.
I tapped into the cigarette lighter for mine. The USBs, Power port, and voltmeter are all powered by it. Using that wiring means that it's only powered when the ignition is on. No running down the battery. Plus there's nothing else being powered by it.

Doesn't a clock need constant 12V, or does it have a battery backup to keep ticking with the key off?