Application Programming Interfaces and dates are just as difficult. Timezone issues crop up because dates and datetimes are just strings in JSON, there's nothing to necessarily say that this is a date in this format.
PHP's time() function returns the current unix timestamp. JavaScript doesn't exactly have the same functionality, but it's pretty close. Put a different and more understandable way, it returns the current time measured in seconds since the Unix Epoch (00:00:00 UTC on 1 January 1970). JavaScript has a similar way of getting the time but it's in milliseconds since the Unix Epoch.