A girl, I sent her a message saying, go to bed early at night. It was sent around 10: 30 in the evening. Why did she reply to me the next day?

Why did this girl reply to you the next day? It means that she went to bed around 10: 30 at night and didn't see the message you sent her at all. It's not that she doesn't want to reply to your message. If she doesn't want to reply, she won't reply you the next day. In fact, you have nothing to worry about on this issue. Go to bed early in the evening, and don't send messages so late. If you want to send it early, she will definitely reply to you because she didn't sleep at all, don't you think?