Importance of graduation on time before a Phd

[SelfMadeEcon]

Just wondering if it is important to graduate on time in your master before applying for a phd. I am starting to think to graduate one year later in my master, in order to complete a double degree, take a break before the "long run" toward a Phd and have the time to prepare a "perfect" GRE.
I know that many people in my Master did not graduate "on time", but they were admitted anyway in the LSE Phd. Do you think that later graduation could bring to disadvantage for application in US?