So about this "Rebirth Potion"

It is not a "Potion of Oblivion" as it does not reset exploration and current level to 1 upon use. Instead it simply makes the "rebirth" function available if it has been less than 6 days and 1 hour from your last rebirth. Meaning you will be able to choose a different talent or change gender like you would a normal rebirth.

Although publicly it is said you have to wait "7 days" to rebirth for free since the new beginnings update, your character can rebirth after 6 days and 1 hour has passed since your last rebirth.