River Song's Diary — ruling 1

You cast the spell as part of the resolution of the last ability. You can't wait and cast the spell at a later time.

River Song's Diary : règles, fonctionnement et interactions (MTG)

River Song's Diary is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Imprint — Whenever a player casts an instant or sorcery spell from their hand, exile it instead of putting it into a graveyard as it resolves. At the beginning of your upkeep, if there are four or more cards exiled with this artifact, choose one of them at random. You may cast it without paying its mana cost.

How it works : River Song's Diary

Original English text — Wizards of the Coast / Scryfall

#1October 13, 2023· Wizards of the Coast
You cast the spell as part of the resolution of the last ability. You can't wait and cast the spell at a later time.
No other card is named in this ruling.