> This is the only sane policy. Timezone conversion must be delayed to the very last moment before displaying time to users.

No, this only works for datetimes in the _past_. For future datetimes you often must store the datetime in the user's (IANA) timezone. Otherwise your application could be off. And your app could be off by more than one hour. In 2011 Samoa moved across the international date line. See https://www.theguardian.com/world/2011/dec/30/samoa-loses-da....