SB Canto 3
The duration of time of three lavas is equal to one nimeṣa, the combination of three nimeṣas makes one kṣaṇa, five kṣaṇas combined together make one kāṣṭhā, and fifteen kāṣṭhās make one laghu.
One kṣaṇa - 8/5 second
SB Cantos 10.14 to 12 (Translations Only)
Śrī Yājñavalkya said: I offer my respectful obeisances to the Supreme Personality of Godhead appearing as the sun. You are present as the controller of the four kinds of living entities, beginning from Brahmā and extending down to the blades of grass. Just as the sky is present both inside and outside every living being, you exist both within the hearts of all as the Supersoul and externally in the form of time. Just as the sky cannot be covered by the clouds present within it, you are never covered by any false material designation. By the flow of years, which are made up of the tiny fragments of time called kṣaṇas, lavas and nimeṣas, you alone maintain this world, drying up the waters and giving them back as rain.