I'd say a few years have passed. The film starts with Thanos taking the Aether from the Collector. The Guardians are called upon urgently by The Collector. He is deeply concerned about Thanos having stolen the Aether, the Tesseract (seen in Thor 3?), and the Time Stone (seen in Captain America 3?). He is aware of the cocoon in his collection that hatched when it was destroyed. He tells them the story about the entity calling himself Magus who has an infinity stone jammed in his forehead.
Magus has been leading the Universal Church of Truth for the last couple years. Thanos is also aware of this entity and is en route. In the ensuing mayhem, the Soul Stone is removed from Magus's possession. Eventually he joins the guardians for a final battle against Thanos and his minions.
By the end of the film Thanos has collected nearly all of the Infinity Stones, setting up Avengers 3 and the giant cosmic crossover. By making Thanos, the head villain, crush the heroes in 3+ films before the finale in Avengers 3 we can see him as the threat he deserves to be.