with or without the definite article

[Fujibei]

I understand "during rush hour" "during sixth period" "during English class" are all without definite article.
If they are correct, why not with the definite article? Any good explanations?

 

[Rover_KE]

Please quote the full sentences in which you found these phrases.

 

[Fujibei]

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During Englishclass, the clock beeped, annoying histeacher. When he brought the device up to her afterward, she told him “it lookslike a bomb,” according to Mohamed.​

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“I told her, ‘Itdoesn’t look like a bomb to me,'” he told the Dallas Morning News.​

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But the Englishteacher kept the clock, and during sixth period, Mohamed was pulled outof class by the principal.
(The Washington Post, 2015.9.16.)​

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[tzfujimino]

In the meantime, I found the full article:
http://www.washingtonpost.com/news/...-after-bringing-a-home-built-clock-to-school/

 

[J&K Tutoring]

There are several rules/conventions for the use of articles. There are different reasons for omitting the in the examples you cited. If you want answers to this kind of question (and I encourage you to seek them!), it would be wise for you to get a copy of Swan's Practical English Usage. You will find the answers to your questions there.

 

[MikeNewYork]

These are all periods of time. A definite article is not needed.