How to charge a newly bought Nexus 5X(lithium polymer)? I just bought a new Nexus 5X, how should I first charge it? (It's a lithium polymer battery)

I plugged it in the charger and the phone turned on. Phone almost had a full charge already though (out of the box).

I usually left my new phones to charge for 12 hours before using them or unplugging them from the charger. Now I know batteries have evolved, so I'm not sure this is beneficial anymore.

I'm not sure what I'm supposed to do for the first charge and it doesn't come with instructions about it.

Any advice?

Thanks!
Charging a new battery for x hours before use is a "legacy hangover" from the days when Nickel Cadmium batteries were used. Those batteries had a "memory effect". As a result, over a period of time, they "remembered" lesser battery capacity than rated capacity. To prevent this, it was advised to always fully charge these batteries
This is not the case with Lithium Ion or Lithium polymer batteries. There is no logic to charge fully or x hours before use. Just use the battery normally, as suggested by others in comments
Table 1 corroborates with additional information