All date fields are returned as ISO-8601 formatted strings.
For example, asking for the creation_time on object 19292868552_522414651110169 returns this:
{
"created_time": "2012-12-15T14:00:02+0000",
"id": "19292868552_522414651110169"
}
You can optionally override the date format by specifying a date_format query parameter. The accepted format strings are identical to those accepted by the php date function.
For example, to retrieve the same ID as above but in Unix time-formatted dates you can add date_format=U:
{
"created_time": 1355580002,
"id": "19292868552_522414651110169"
}