ISO-8601 is not the correct format for serializing local time unless it's in the past.
In my experience, a local datetime picker is going to be used almost exclusively for a future date and time. What you want instead of a timezone offset is a zone ID. That way date and tzdata can handle it properly on the backend.
In my experience, a local datetime picker is going to be used almost exclusively for a future date and time. What you want instead of a timezone offset is a zone ID. That way date and tzdata can handle it properly on the backend.