Thread:Hey1234/@comment-4274013-20181113024829

Maleficent said

1. Before the sun sets 2. on her 16th birthday

specifically in that order.

That's not a specific day, that's a time period - between after Maleficent cast the curse and the last sunlight on Aurora's 16th birthday. That makes 16 years during which at any given moment Maleficent could have fulfiled her curse. That's why the princess had to be hidden immediately and why the people are happy and Maleficent angry that her evil prophecy did not come to fruition during all those years. 