Do the same trick for TIME. The same three constants — ħ, G, c — combine one and only one way into a duration: the Planck time, about 5×10⁻⁴⁴ seconds. It’s how long light takes to cross a Planck length, and the earliest moment after the Big Bang that physics can even talk about. A unit of time that falls out with no clock. Slide down the ladder of durations.
The Planck time tₚ = √(ħG/c⁵) ≈ 5.39×10⁻⁴⁴ s is the unique DURATION built from ħ, G, c — equal to ℓₚ/c, the light-crossing time of a Planck length. It is the conventional lower bound before which the classical notion of time is not expected to apply (the ‘Planck epoch’). Like the Planck length it is a natural unit that falls out of the constants, not measured off any clock. A fail-loud self-check throws unless √(ħG/c⁵) lands between 4 and 7 ×10⁻⁴⁴ s. ◆ real physics, node-verified.
The value is exact; ‘time has no meaning before tₚ’ is the standard expectation, not proven. The unit falling out of the constants is the real content.