This is a sentence from Mao Zedong.
Yan Zhenqing’s poem is “The lights are on at three o’clock and the rooster is on at five o’clock, which is when men are studying. Black-haired people don’t know how to study early, and white-headed people regret studying late.”
“Why bother if you are persistent? Sleeping at three o'clock and getting up at five o'clock; the most useless thing is to be exposed to cold for ten days in one day." This is a couplet written by Mao Zedong based on Yan Zhenqing's poem.
It means that as long as you have perseverance, there is no need to get up early and go to bed late every day (to do things). The worst thing is to work for one day and rest for ten days.