Time Measurement starts with ParamanuKaala.
Where, Paramanukaala is the time taken by the SUN to pass a ‘PARAMANU‘.

PARAMANU – is the Ultimate particle that
which cannot be reduced any further.
PARAMANU or ‘the smallest atom’, is also
the basic building-block of the material universe.

Quoting from Srimad Bhagavata Purana, which gives details about how time is measured, as in Vedic system.

So, PARAMANUKALA, is ‘a base unit of time’, required by the SUN to pass ‘a base unit of the material’ called ‘PARAMANU‘.

2 Paramanu together is an ‘Anu‘; 3 such anu’s make a ‘Trasarenu‘; 3 Trasarenu is a ‘Truti‘; 100 Truti is a ‘Vedha‘;3 Vedha is 1 Lava; 3 such Lava is a ‘Nimesha‘(moment); 3 such Moments is a ‘kshana‘; 5 kshana is a ‘Kaashtha‘; 15 kaashtha equals a ‘Laghu‘;15 Laghu makes 1 Nadika or 24 mins approximately; 2 Nadika(Nazhigai in Tamil, Ghatika as in north indian usage) makes one ‘Muhurtha‘, approximately 48 mins. 6 or 7 nadikas makes one Yaama. To have an understanding of a complete Creative and dissolution cycle of the entire universe, the following picture explains the same.