It's a part of ISO-8601 date representation. It's incomplete because a complete date representation in this pattern should also contains the date:
2015-03-04T00:00:00.000Z //Complete ISO-8601 date
If you try to parse this date as it is you will receive an Invalid Date error:
new Date('T00:00:00.000Z'); // Invalid Date
So, I guess the way to parse a timestamp in this format is to concat with any date
new Date('2015-03-04T00:00:00.000Z'); // Valid Date
Then you can extract only the part you want (timestamp part)
var d = new Date('2015-03-04T00:00:00.000Z');
console.log(d.getUTCHours()); // Hours
console.log(d.getUTCMinutes());
console.log(d.getUTCSeconds());