UTC (or Unix timestamp, or any other non-localized date-time format) doesn't work for future localized events. It's fundamentally impossible to say what will be the UTC timestamp which corresponds to 9AM in some particular location in the future: the timezone of that location could arbitrarily change between now and then. Countries and smaller areas often experiment with such changes, wars happen and conquerors/liberators change the time etc.
So, when possible, it's best to store (future) human events in a localized datetime string. For things like physical events, the opposite is true of course - you can't say what will be the local date and time when the Sun will hit high noon over Athens 10 years from now, but you can certainly calculate the UTC timestamp for that.
So, when possible, it's best to store (future) human events in a localized datetime string. For things like physical events, the opposite is true of course - you can't say what will be the local date and time when the Sun will hit high noon over Athens 10 years from now, but you can certainly calculate the UTC timestamp for that.