"One person. All it takes is one person. I couldn't save Harry for Lily. So now I give my allegiance to the cause she believed in. And it's possible - that along the way I started believing in it myself."
-- Severus Snape (CC3.9)
Ron Weasley is in pain on the return from using the Experimental Time-Turner at the First Task. He and Hermione Granger are caught by the Dementors, as they allow Severus Snape and Scorpius Malfoy to escape. However, Snape is stopped by Dolores Umbridge – but he successfully defeats her in a duel (CC3.9).
However, the delay allows the Dementors to catch up with Snape and Scorpius. Snape, thinking of his love for Lily and knowing there is a world where her son lives, gives Scorpius the time to go back in time.
24 February 1995
Scorpius and Albus are taken back to the present time and are confronted by their parents – Harry Potter, Ginny Weasley and Draco Malfoy – accompanied by Headteacher McGonagall. Caught “in the act” but thinking quickly, Scorpius says he has lost the Experimental Time-Turner (CC3.9).
Immediately after the previous event in the 2020 of the Scorpion King timeline, then back in time to February 1995 during Second Task and finally back to 2020 (pre Time-Turner use)
This event takes place in the Half Repaired timeline (initially during the Scorpion King timeline and then during the Roseless timeline), as described in the essay "Albus Potter and the lesson in Quantum Mechanics" by Nick Moline.
We are again shown the depth of the love between Hermione Granger and Ron Weasley, and the scene of them being taken by the Dementors is extremely chilling and tragic to watch. We also see again the heroic sacrifice of Severus Snape, as his soul ripped from him by the Dementors (CC3.9).
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: Harry Potter and the Cursed Child, Parts One and Two