What Kulver said.
What might be midnight for you, is most likely morning at someone else's place. There's many unspoken laws and rules of IRC. One of them being; If there's no activity, write someone and WAIT. Too many log on, write something and disconnects again because they didn't get a reply within the first 5 minutes. Most people are online on IRC the whole day (idling) and simply doesn't check it every 5 minute. In worst case, you can highlight someone, if you want their attention. But you might want to be a bit cautious about that, people generally don't want to get highlighted for nothing.
Sorry for my horrible grammar ^ - I just woke up.