Because Albus Potter has been forbidden by his father Harry from associating with Scorpius Malfoy, they are going through their daily lives at Hogwarts without each other. When they see each other on the staircases of Hogwarts, there aren’t any words spoken, just great sadness and grief emanating from them both (CC2.12).
Probably 1 or 2 days after the previous event, early September 2020
This event takes place during the Roseless timeline, as described in the essay "Albus Potter and the lesson in Quantum Mechanics" by Nick Moline.
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 31 July 2016, with Sam Clemmett in the role of Albus Potter and Anthony Boyle as Scorpius Malfoy: Harry Potter and the Cursed Child, Parts One and Two