Above is the Doyalist reason, and almost certainly the root reason.
The Watsonian reason was that it would force Voldemort to waste an hour in the preparation, making any attempt to steal the Stone take an hour longer. As traps go, it’s reasonably clever.
The potion did serve its in-story purpose of banishing the flames blocking the doorway, after all, so it’s not like Voldemort spent that time on the potion and then used his wand to take care of the flames.
It was an excuse to have two characters talk about the plot—doesn’t seem like there was anything more to it.
Above is the Doyalist reason, and almost certainly the root reason.
The Watsonian reason was that it would force Voldemort to waste an hour in the preparation, making any attempt to steal the Stone take an hour longer. As traps go, it’s reasonably clever.
The potion did serve its in-story purpose of banishing the flames blocking the doorway, after all, so it’s not like Voldemort spent that time on the potion and then used his wand to take care of the flames.