"'Dad. Help. Godric’s Hollow. 31/10/81.' It's a message. Clever boy left me a message."
-- Harry Potter (CC4.6)
31 October 2020
Sitting with his old baby blanket and remembering his parents – as he does every year on Hallow’s Eve, Harry Potter is joined by his wife Ginny in Albus’s room. As they look at the blanket, Harry sees the holes that the Love Potion made when Albus threw his gifts away (CC1.7). Ginny realises the holes are forming words and deciphers the message that Albus has sent from the past (CC4.6).
31 October 1981
Simultaneously we hear Albus and Scorpius Malfoy drafting the message and putting it onto the blanket (CC4.6).
All Hallows Eve - 31st October 2020, simultaneously with 31st October 1981
This event takes place during the Voldemort Final timeline, as described in the essay "Albus Potter and the lesson in Quantum Mechanics" by Nick Moline.
Harry's eyesight is so bad, Ginny is able to read the letters on the message first. She also apologises to Harry for blaming him for Albus running away - Albus was, after all, being enticed away by the daughter of Lord Voldemort, a "powerful dark witch" (CC4.6).
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 with Jamie Parker in the role of Harry Potter, Poppy Miller as Ginny Weasley, Sam Clemmett as Albus Potter and Anthony Boyle as Scorpius Malfoy: Harry Potter and the Cursed Child, Parts One and Two