The lifetime of white hole remnants is $M^5$

The black-to-white hole scenario is a well-motivated proposal from non-perturbative quantum gravity concerning the final stage of black hole evaporation. In this framework, a black hole of initial mass $M$ undergoes Hawking evaporation over a timescale of order $M^3$ before tunneling into a long-lived white hole. Previous estimates suggest that the lifetime of the resulting white hole scales as $M^4$. In this short note, I argue that such estimates neglect key aspects of the white hole's internal dynamics, and I demonstrate that a more consistent timescale for the white hole lifetime is of order $M^5$.