I've discovered that when I have to teach a class, I will often do a concept map myself, to see how well I know a topic. Often I discover that I really don't have a grasp on an issue. I don't know where this fits in my scheme of information. Then I have to go back and do some more research. It is actually an instructor's tool as well as an instruction tool.
Concept mapping is an extremely good evaluation tool.
But in my semester-long class, we have one every class, with maybe two exceptions. And we have a pre and a post map. Before I cover a topic, the students do a concept map for me. And as I am picking them up, I evaluate them. That's how fast you can do it.