排定的開演時間
這是那條分界線本來待的地方：票上印的、網站上列的那個時間點。
noun · B1
The time at which a film, play, concert or other public performance is set to begin.
開演時間
核心畫面
One way to hold showtime: the house lights go down, the talking stops, and the curtain moves. Up to that second everything was preparation — tickets, seats, tuning, waiting. After that second, people are watching and the thing itself is happening. Showtime is that dividing second, first on a real theatre clock, and then anywhere at all.
showtime 的核心畫面可以想成：場燈暗下來，說話聲停了，布幕開始動。在那一秒之前，全部都是準備——買票、入座、…更多收起
showtime 的核心畫面可以想成：場燈暗下來，說話聲停了，布幕開始動。在那一秒之前，全部都是準備——買票、入座、調音、等待。在那一秒之後，有人在看，事情真的開始了。showtime 就是那一秒的分界線。它先是戲院時鐘上的一個刻度，後來被搬到任何地方去用。From the word’s history
The source records showtime as simply show + time. The two parts say the whole thing: the time at which the show begins.
來源記載 showtime 就是 show 加 time。兩個部分合起來就說完了：表演開始的那個時間。這也是為什麼它後來可以被借去講任何「該開始了」的時刻——只要把「表演」換成你正要做的那件事，畫面完全不用改。
Wiktionary entry for showtime, etymology_text in supplied packet (kaikki:3f6f69a190036ae4:1389096649)
Two branches
該動真格的時刻
同一條分界線被搬離戲院：準備在線的這一邊，真正要做的事在另一邊，而且有人在看。
noun · B2
The moment when the waiting and the preparing stop and the real activity has to start. The source marks it as informal American English, and it is used about anything important that is about to begin, not only a performance.
該上場了；動真格的時刻