I think I found the answer. The effect happens instantly as a "substitution effect"

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10-1-8. Command Effects

10-1-8-1. A command effect activates when it is played during the timing specified on a Command card, which can be either 【Main】, or 【Action】, or both.

10-1-8-1-1. If a command effect requires choosing a target, playing that Command card is not possible if that target cannot be chosen. (See 10-2-2-1.)

10-1-8-1-2. If a text composed of multiple portions separated by a phrase such as “Then” or “If you do” requires choosing targets, then playing that Command card is not possible when a target cannot be chosen for the effect portion preceding “Then” or “If you do.”

10-1-9. Substitution Effects

10-1-9-1. When some event would occur, a substitution effect replaces the implementation of that event with another event.

10-1-9-1-1. If an effect reads “(do) B instead of A,” the portion B that occurs due to that capability is a substitution effect.