No, they won't kill you. Also, I have to disagree with the other answer regarding them being not a great idea before bed. Oranges do have carbs, but there's not much evidence that they have enough carbs to harm your sleeping patterns. Also, carbs, themselves, don't do much to your sleeping patterns, much like sugar doesn't actually make kids "wired" or "hyper."
If oranges did anything to you by eating them near bedtime, that may depend on your general health. If you're prone to acid reflux, for example, oranges might cause an increased supply of acid, causing your reflux to worsen, especially when you're laying down. For people who have sensitivity to acidic foods, naturally, an orange might be a problem to eat at anytime. Outside of that, though, it is unlikely that an orange before bed is going to harm you.