If a humanoid or beast dies, can a Spores druid wait until their own turn to use the Fungal Infestation reaction feature to animate them as a zombie?

Question

Circle of Spores druids gain the Fungal Infestation feature at 6th level. Its description states, in part (GGtR, p. 27):

If a beast or humanoid that is Small or Medium dies within 10 feet of you, you can use your reaction to animate it, causing it to stand up immediately with 1 hit point. The creature uses the zombie stat block in the Monster Manual. It remains animate for 1 hour, after which time it collapses and dies.

If a beast or humanoid (e.g. a bandit) dies within 10 feet of a Circle of Spores druid, and the druid doesn't use Fungal Infestation right away to animate them as a zombie (e.g. if the druid already spent their reaction earlier in the round, or whatever), can the druid wait until their next turn to use a reaction to animate the dead creature as a zombie?

Answer 1

No, it must be used the moment the creature dies.

The rules for reactions say (PHB, pg. 190; emphasis mine):

A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

If you wait until your next turn, you can no longer use your reaction, as the trigger has passed - doing so would not be an instant response to the trigger, but a rather slow response. Using a reaction requires that you instantly respond to the trigger.