There might be more to it than that. He said that there was a delay? He chose someone, Akane, the first week, but nothing immediately happened. So he supposedly thought something interfered, so he chose to lower someone's else GPA the next week. But that same week, it finally hit Akane.

[ in other words, you don't see what happens to the person until the week after you choose them, if light's telling the truth. ]

From what I heard, he's going to choose to help someone this week instead.