What is the meaning of Instant Restoration's duration of 1 round/level?

Question

The spell Instant Restoration seems, at face value, like it is a one-time cast spell with no need for a duration. The spell stops a summoned creature from dying, gives it 4d8+(1*CL) hp, and that seems like the end of it.

The wording on this one seems very clear until I look at the duration.

It appears that the spell lasts 1 round per level. The only things I can assume by this, is that it either

1. Heals the healing amount every turn, which seems absurd, for its level. Or
2. The creature, in question, dies as it would have normally, after the spell's duration is over.

However, it says no such thing in the description, and even goes out of its way to mention

"it remains as if its hit points had never dropped to 0 or fewer".

so, I see nothing specifically indicating that this would be the case. Most spells try to go out of their way and explain what happens at the end of a duration, explicitly, which leads me to believe this is a typo, of some sort.

Answer 1

For lack of a better answer, that seems to be a typo.

Everything you note about the ability is true and consistent with its entry in Archives of Nethys, which should reflect the most current, correct details due to their SRD agreement with Paizo.

• Casting Time 1 immediate action
• cast "when a summoned creature you control drops to 0 or fewer hit points."
• the creature is healed for 4d8 hp + 1 hit point per caster level. If this healing brings your summoned creature’s hit point total to 1 or more hit points, it remains as if its hit points had never dropped to 0 or fewer.

Nothing about this spell requires a Duration, and the spell provides healing, not temporary hit points, so there's no reason to think they would be removed if the spell ends. Nothing seems to prevent the summoned creature from being defeated and disappearing if those hit points are lost again.

I would hazard to guess that a previous version of the spell was cast ahead of time (probably as a Standard action) and triggered if the creature was brought to 0 hit points, similar to the Feat Reactive Healing. In my hypothetical, they might have changed it in editing, deciding that they wanted it to move it to the spellcaster's Immediate action but forgot to delete the Duration line.