1 don't do it, or don't rest (idiom); either give up, or go through to the end
2 Since we started, we must carry it through whatever happens.
3 in for a penny, in for a pound
一日三秋
yī rì sān qiū
1 a single day apart seems like three seasons (idiom)
一日不见，如隔三秋
yī rì bù jiàn , rú gé sān qiū
1 one day apart seems like three years (idiom)
一日之计在于晨
yī rì zhī jì zài yú chén
1 make your day's plan early in the morning (idiom)
2 early morning is the golden time of the day
一日之雅
yī rì zhī yǎ
1 lit. friends for a day (idiom)
2 fig. casual acquaintance
一日千里
yī rì qiān lǐ
1 lit. one day, a thousand miles (idiom); rapid progress
一日为师，终身为父
yī rì wéi shī , zhōng shēn wéi fù
1 lit. teacher for one day, father for ever (idiom)
一醉方休
yī zuì fāng xiū
1 to get thoroughly drunk (idiom)
2 to get plastered
不可同日而语
bù kě tóng rì ér yǔ
1 lit. mustn't speak of two things on the same day (idiom); not to be mentioned in the same breath
2 incomparable
不眠不休
bù mián bù xiū
1 without stopping to sleep or have a rest (idiom)
不见天日
bù jiàn tiān rì
1 all black, no daylight (idiom); a world without justice
世风日下
shì fēng rì xià
1 public morals are degenerating with each passing day (idiom)
今日事今日毕
jīn rì shì jīn rì bì
1 never put off until tomorrow what you can do today (idiom)
休戚相关
xiū qī xiāng guān
1 to share the same interests (idiom)
2 to be closely related
3 to be in the same boat
来日方长
lái rì fāng cháng
1 the future is long (idiom); there will be ample time for that later
2 We'll cross that bridge when we get there
偷天换日
tōu tiān huàn rì
1 to engage in fraudulent activities (idiom)
2 skulduggery
3 to hoodwink people
4 to cheat sb audaciously
光天化日
guāng tiān huà rì
1 the full light of day (idiom)
2 fig. peace and prosperity
3 in broad daylight
冰冻三尺，非一日之寒
bīng dòng sān chǐ , fēi yī rì zhī hán
1 three feet of ice does not form in a single day (idiom); Rome wasn't built in a day
同日而语
tóng rì ér yǔ
1 lit. to speak of two things on the same day (idiom); to mention things on equal terms (often with negatives: you can't mention X at the same time as Y)
在家千日好，出门一时难
zài jiā qiān rì hǎo , chū mén yī shí nán
1 lit. at home, one can spend a thousand days in comfort, but spending a day away from home can be challenging (idiom)