I think you mean they are adding extra time:
From the Summer Double XP announcement (6/27)
Double XP is back for an entire week!
Whether you’re a new or experienced player, take advantage of Double XP and Legacy XP to level up your main character faster or to create an alternate character and enjoy a new class story and gameplay!
Double XP and Legacy XP will be active during the following time:
•Starts: July 1, 2014 (11AM PDT / 6PM GMT)
•Ends: July 7, 2014 (12AM PDT / 7AM GMT)
From the Patch 2.8.1 Patch notes:
Progress faster with a Double XP Week! Get twice the experience from July 1st 18:00 GMT (11:00 PDT) to July 8th 07:00 GMT (00:00 PDT).
That a whole 24 hours more.