Understanding how a vast number of neuron types derive from a limited number of neural progenitors remains a major challenge in developmental neurobiology. In the post-embryonic Drosophila brain, specific neuron types derive from specific progenitors at specific times. This suggests involvement of time-dependent cell fate determinants acting as 'temporal codes' along with lineage cues to specify neuronal cell fates. Interestingly, such temporal codes might be provided not only by several regulators acting in sequence, but also by the differential protein levels of the BTB-zinc finger nuclear protein Chinmo. Identifying temporal codes and determining their origins should allow us to elucidate how neuronal diversification occurs through protracted neurogenesis.