What does Ky mean when he tells Cassia they are running out of time and how does he feel about the decision Cassia made for him at his workplace?

When they are hiking for nearly the last time, Ky mentions that they are running out of time. He means time together, time for Society, and time for hiking. Change is all around them. He shares with Cassia the fact that he knows about the sorting and he also knows about the Match. While he might not agree with Cassia's decisions, he trusts that she always made her choices out of love, doing her best to find the best for him.