Data that is tracked by the Android Application / Wear-Device is sent to the server using a specific data model based on JSON.
It contains information about the user, the data that has been tracked and a timestamp. The user is described by its prename, name, sex and age. The tracked data currently consists of the heartrate, but can be extended in the future.
Timestamps should be saved according to ISO8601 which means yyyy-mm-ddThh:mm:ss or as an example 2014-11-25T10:20:37. You can read more about ISO8601 here
There is an example you can take a look at here