Niantic has updated an official known issues support page for Pokémon GO. Read on below to learn more:
Time format displaying in 12h in unsupported languages
Last Updated: 2d
Issue Description: Trainers playing Pokémon GO using devices with unsupported languages may see the in-app time displayed in 12h format, even if their device settings are set to use 24h.
Issue Status: Resolved.
Source: Official Pokémon GO support page