My intuition is telling me that since the last level of hell is some kind of a mathematical limit of how stupid a person can get (or how annoying or how evil), there must be a parallel with Planck units, which are the minimum measurable amounts of physical quantities. (or equivalently, maximum, when considered how many you can fit in something else) The Planck time, in this context, to be precise.
What is the statistically average duration of a birth in Naraka, the non-stop hell? We could consider that a sort of Planck-lifetime of a being, especially since to the outside observer, a hell lasting billions of years might look much shorter than for the being in hell. Therefore, the Planck-lifetime of a hell being during a single rebirth might actually be comparably short as the physical Planck-time when observed from the outside.