transaction.date in google-iap-v3 - what is it?

What format is transaction.date when using Google IAP v3 plugin? It is not a parsable date string as assumed in http://coronalabs.com/blog/2013/09/03/tutorial-understanding-in-app-purchases/ It is just a big number but it is not unix timestamp. Few minutes ago I got 1411668847128 as transaction.time. These are test purchases if that makes any difference.