Timezone indicates where the time is set. The date/time (we can call it timestamp) could not be understood by the other side when there are not enough information.

If the client (browser) receives a timestamp from the backend, it should take into account the origin timezone (the date/time should be expressed in UTC format and the timezone of the browser to represent the timestamp in the client local time. When submitting the data, the client can also send either the local time+ timezone or the timestamp normalized in UTC format (recommended; please have a look at the W3C guidelines in http://www.w3.org/International/wiki/WorkingWithTimeZones).