Every schedule in a theatre is written in the wrong direction on purpose.
There is exactly one time in the day that cannot move: the curtain goes up at seven. Everything else is worked out from there, backwards, one step at a time. The doors open half an hour before the audience is seated, so the doors open at half past six. The stage must be clear before the doors open, so the sound check has to be finished by six. A sound check takes forty-five minutes, so it begins at a quarter past five.
The actors are called an hour before that, at a quarter past four, which means the set has to be built and the floor swept by four — and so, at last, the crew's start time appears at the bottom of the page: one o'clock, four hours before anyone would have guessed.
Nothing on that sheet was decided by starting at the beginning. Had the manager begun at one and worked forwards, she would have had to guess how long each job takes and hope the total landed on seven. Instead she started from the only fixed point she had and let each step tell her the one before it.
It is the same move a good test-taker makes with a multiple-choice question. The answer is already printed on the page. Rather than building a solution forwards and hoping it lands on one of the four, you can begin at the finish and check which one fits.
The curtain has never once gone up late.