日夜奋战的英文：
struggle hard day and night

参考例句：

The whole village has been working day and night gathering and threshing this year's crop,
全村的人都日夜奋战，为了把今年的庄稼收获上来，打完场，

struggle是什么意思：
v. 奋斗，努力；艰难地行进；斗争，搏斗；艰难地做；尽力；挣扎；争夺
n. 斗争，竞争；奋斗，努力；难事；打斗

struggling artist
努力奋斗的艺术家

The two leaders are struggling for power.
那两个领导人正在争夺权力。

She struggled to free herself.
她挣扎着以求脱身。

hard是什么意思：
adj. 硬的，坚固的；困难的；有力的；冷酷无情的
adv. 努力地；困难地；严重地，猛烈地

It is hard to conclude.
这很难断定。

It is blowing hard.
风刮得很大。

It was sleeting hard.
雨雪霏霏。

day是什么意思：
n. 一天；白昼，白天；工作日；时代，时期

Things go on day by day.
事情逐日进行着。

Day by day the situation is improving.
情况在一天天地好转。

Like this, day after day.
就这样，日复一日。