A timezone can’t be encoded with a Unix time stamp, or a date without a time, or just a time. Unix timestamps ignore leap seconds and treat days as 86400 second

A timezone can’t be encoded with a Unix time stamp, or a date without a time, or just a time. Unix timestamps ignore leap seconds and treat days as 86400 seconds, so it doesn’t correspond directly to UTC. And they aren’t readable by humans. There are many reasons Unix timestamps aren’t appropriate for encoding a date and time.