Read Time Strangeness

I sent 4 messages at the same time to someone. When I look on the chat screen the delivery time is the same but the read time is all over the place. I think the fourth one was read first, then the first a couple hours later, third later still and second even later. How does that happen? If it's delivered how can they be getting read at such different times? Were my messages actually delivered at random times or is the read time just incorrect? all other messages are normal.