Cooking with them guarantees a crit, boosting the effect of the other ingredients you mix it with. It’s like cooking with fairies, or in the last half hour before midnight on a blood moon night.
In addition to that, "Baked Golden Apple" is a different dish than just "Baked Apple", so if you're someone who wants to complete the recipe section, you have to roast one of those at least once.
It's not just the last half hour, it's the hour around midnight,11:30-12:30. Everybody thinks it ends at midnight because there's the cutscene and then the creepy music notes and wispy malice (or gloom?) effects stop, but you've still got thirty golden seconds.