Meaning:

“修” is short for “修炼,” which originally referred to the practice of Taoists who tried to make pills of immortality and boost their energy, and “仙” means “immortal.” There are numerous games and Internet-published novels embraced by Chinese young people whose main characters are immortals, but most recently Chinese netizens have used the term in a totally different sense. A popular meme with the caption “熬夜修仙” (stay up late to make efforts toward immortality) has led people to use “修仙” jokingly to mean “stay up late.”

Example:

A: 你昨晚几点睡的啊？一点还发了朋友圈。

Nǐ zuówǎn jǐdiǎn shuì de a？ Yīdiǎn hái fā le péngyǒuquān。

When did you go to bed last night? I found you refreshed your WeChat Moments at 1 a.m.

B: 差不多凌晨两点。我玩游戏忘了时间。

Chàbùduō língchén liǎngdiǎn。 Wǒ wán yóuxì wàng le shíjiān。

I went to bed at around 2 a.m. I forgot about the time playing games.

A: 你这样修仙可不行。

Nǐ zhèyàng xīuxiān kě bùxíng。

You’d better not stay up so late.