"I was more worried about her being eaten by a bookcase! Find. Something. Anything..."
-- Albus Potter (CC1.19)
The bookshelves, which are full of dangerous books, are a “Weaponised Library” and fight back. Scorpius, Albus and Delphi have to solve the Time-Turner Book Riddles to be able to rescue themselves and find the hidden Time-Turner (CC1.19).
This is the day after Albus and Scorpius escape from the Hogwarts Express and visit the St Oswald's Home - so during 2 September 2020.
It is interesting that being captured and taken into the Weaponised Library causes the Polyjuice Potion to wear off.
From the Web
Pottermore: Harry Potter and the Cursed Child
The theatre production opened in the West End of London at the Palace Theatre on 30 July 2016, with Esther Smith in the role of Delphi, Anthony Boyle as Scorpius Malfoy and Sam Clemmett as Albus Potter: Harry Potter and the Cursed Child, Parts One and Two