There are various theories as to the length of setsuna, however it is said that there are 65 setsuna in the space of one click of the fingers, and also in the "Mahavibhasa-sastra" (a Buddhist document) it states that 24 hours = 30 mukoritta (1 mukoritta is 2880 seconds) = 900 robaku (1 robaku is 96 seconds) = 54,000 tasetsuna (1 tasetsuna is 1.6 seconds) = 6,480,000 setsuna and the length of one setsuna is 1/75th of a second.
刹那の長さについては諸説あるが、指をひとはじきする（弾指）間に65刹那あると言われているほか、『大毘婆沙論』では、24時間30牟呼栗多900臘縛54,000怛刹那6,480,000刹那とし、1刹那の長さを1/75秒に比定している。