When they fought over the Time Turner it seems to have landed them all in 1981.
SCORPIUS: The Time-Turner is spinning . . . Look at what she’s doing . . . She can’t leave us behind.
ALBUS and SCORPIUS both scramble to grab part of the Time-Turner.
And there is a giant whoosh of light. A smash of noise.
And time stops. And then it turns over, thinks a bit, and begins spooling backwards, slow at first . .
And then it speeds up.
When Delphi smashed the Time Turner it stranded them there. The five minute rule no longer applies.
SCORPIUS: Albus . . .
ALBUS: What have we done?
SCORPIUS: We had to go with the Time-Turner, we had to try to stop her.
DELPHI: Stop me? How do you think you’ve stopped me? I am done with this. You may have destroyed my chances of using Cedric to darken
the world but maybe you’re right, Scorpius — maybe prophecies can be
prevented, maybe prophecies can be broken. What is undoubtedly true
is: I’m done with trying to use you annoying, incompetent creatures
for anything. No more wasting precious seconds on either of you. Time
to try something new.
She crushes the Time-Turner. It explodes in a thousand pieces.
DELPHI ascends again into the air. She laughs in delight as she sets
off hard away.
The boys try to chase her, but they’ve not the slightest chance. She
flies, they run.
ALBUS: No . . . No . . . You can’t . . .
SCORPIUS turns back and tries to pick up the Time-Turner pieces.
The Time-Turner? It’s destroyed?
SCORPIUS: Utterly. We’re stuck here. In time. Wherever in time we are. Whatever it is she’s planning to do.
Cursed Child - Act 3, Scene 20