No. The people make the mess. For persistence, only UTC without timezone makes sense. For UI, with few exceptions, only local time without time zone in ISO 8601

No. The people make the mess. For persistence, only UTC without timezone makes sense. For UI, with few exceptions, only local time without time zone in ISO 8601 makes sense. The only not so easy decision is: is it better to store as Unix epoch or as ISO string. That is a tradeoff between compactness and easy searching of date/time ranges.