Skandapurana 16.105.33

16.105.33

dinamānaṃ pravakṣyāmi brahmaṇo lokakartṛṇaḥ ..
netrabhāgāccaturbhāgastruṭiḥ kālo nigadyate .. 33 ..

I shall declare the measure of a day of Brahmā, the creator of the worlds:
a fourth part of an eye's wink is said to be the unit of time called a truṭi.