Required for the production of circadian rhythms. The biological cycle depends on the rhythmic formation and nuclear localization of the TIM-PER complex. Light induces the degradation of TIM, which promotes elimination of PER. Nuclear activity of the heterodimer coordinatively regulates PER and TIM transcription through a negative feedback loop. Behaves as a negative element in circadian transcriptional loop. Does not appear to bind DNA, suggesting indirect transcriptional inhibition (By similarity). Forms a heterodimer with period (PER); the complex then translocates into the nucleus. Nuclear at specific periods of the day. First accumulates in the perinuclear region about one hour before translocation into the nucleus. Interaction with per is required for nuclear localization (By similarity). Contains a 32 AA domain highly conserved between species. Deletion of this domain leads to long-period phenotype and arrhythmia (By similarity). Phosphorylated with a circadian rhythmicity. Belongs to the timeless family.