Answer: The description of the time as "H-Hour" and the general "shepherding" in the professor reveals the seriousness of the impending situation.
In this passage, the general and the professor are contrasted. The way the general behaves shows the importance of the situation. He refers to the time as "H-Hour" and the author tells us that he "shepherd" the professor in. Nevertheless, the professor, while perhaps also worried about the situation, is dressed in comfortable, casual clothes. This provides a contrast to the urgency and seriousness of the general.