tzs for Jawbone Moves

I would like some clarification on tzs for the Jawbone Moves endpoint: https://jawbone.com/up/developer/endpoints/moves. Is this key going to be present on all response items? If not, what types of records will have it vs those that don't. Additionally, the docs indicate it will be an array of arrays with the following format:

"tzs": [
            [1384963500, "America/Phoenix"],
            [1385055720, "America/Los_Angeles"]
        ]

However, I am getting response that look like the following:

"tzs": [[1468410383, -14400]]

Is the second an offset I presume in seconds?

The tzs key will appear in responses from the moves endpoint that provide data for a given day's move. It will always be present, but it will only contain more than one entry if the user changes timezones during the given time period (e.g., the user is travelling).

Here's the explanation from the documentation:

Each entry in the list contains a unix timestamp and a timezone. In most instances the timezone entry is a string containing the Olson timezone.

When the timezone entry is just a number, then you are correct it's the GMT offset in seconds, so -14400 corresponds to US/Eastern