Opens are returned as a feed of DateTime objects with counts next to them. These timestamps represent the beginning of an hour period, and the count is the number of opens that happened in that hour.
This API endpoint uses the ISO 8601 DateTime format.
2015-07-25T00:00:00.000+00:00(Date, Time, Offset)
Note: When running the curl command with parameters, you should wrap the URL in double quotation marks.