Citta-kkhana: 'consciousness-moment', is the time occupied by one single stage in the perceptual process or cognitive series cittavīthi see: viññāna-kicca This moment again is subdivided into the genetic uppāda static thiti and dissolving bhanga moment. One such moment is said in the commentaries to be of inconceivably short duration and to last not longer than the billionth part of the time occupied by a flash of lightning. However that may be, we ourselves know from experience that it is possible within one single second to dream of innumerable things and events. In A. I, 10 it is said:;Nothing, o Bhikkhus, do I know that changes so rapidly as consciousness. Scarcely anything may be found that could be compared with this so rapidly changing consciousness.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.