In North Indian Classical music, each raga has been traditionally associated with a performance time, which supposedly maximizes its aesthetic and emotional effects on the listener. The objective of this work was to investigate the structural basis, if any, for the association of ragas with different times of the 24-hour span. The tonnetz framework has been used to analyze the pitch sets of 65 North Indian Classical ragas, and structural similarities have been observed between ragas associated with (1) times of transition between day and night, i.e., dawn and dusk, and (2) times between these transitions. These findings could provide some insight into the scientific basis of the age-old raga-time relation, and their effects on the perception of the listener.