The sentence that stresses on the time is:
It is important to be in class on time.
This sentence emphasizes the importance of being in class at the specified time. The phrase "on time" clearly indicates that punctuality is crucial. The other two sentences, while also conveying the importance of attending class, do not explicitly emphasize the significance of being punctual.
Here's a more detailed breakdown of each sentence:
It is important that you be in class.
This sentence focuses on the general importance of attending class, but it doesn't explicitly mention the timing of attendance. While punctuality might be implied, the emphasis is more on the act of being present in class.
It is important to be in class on time.
This sentence highlights both the importance of attending class and the significance of being punctual. The phrase "on time" underscores the importance of adhering to the specified schedule and not being late.
It is important that you be in class on time.
Similar to the second sentence, this sentence emphasizes both the importance of attendance and punctuality. The phrase "that you be in class on time" places a stronger emphasis on the timing of attendance, suggesting that being punctual is an essential aspect of being in class.
Therefore, the sentence that most strongly stresses on the importance of punctuality is: It is important to be in class on time.