Ratriman
It indicates length of the night, i.e. the period from sunset to sunrise. It is also measured in hours, minutes and seconds (ghatis, palas, vipalas).
Dinman + Ratriman = 24 hours = 60 ghatis = 24 x 60 minutes = 60 x 60 palas
Everyday there is change in Dinman and Ratriman.