Does the Islamic 24-hour clock start at maghrib in countries that practice the Islamic calendar? If not, why?

I understand the Islamic day begins at sunset/maghrib (e.g. https://islam.stackexchange.com/questions/24725/if-the-date-changes-with-sunset-why-is-asr-called-the-middle-prayer) . However, it is less clear whether the daily 24 hour clock also begins (i.e. 00:00 (0 hours and 0 minutes)) at this time, as practised by countries or major international organisations which adopt the Islamic calendar. I would be grateful if members here could inform as to the whether it does? And if not (e.g. it starts at the (Gregorian calendar) midnight), why this is the case? That is, the justifications (especially theological/fiqh (vs practical/logistical) for the discrepancy between the accepted theological basis of the start of the day, and the actual practice?. Thank you.