Following Fig. 6 and 7, we show the influence of an earlier/later bar formation epoch on the NSD gas chemical evolution. The middle row of the onfall scenario shows the overabundance of the gas feeding the NSD and is the same for both models. The bottom middle and right panel hereby focus on an early bar formation time. The bottom left overlays the evolution of a single ring (at R = 55.5 pc) for all three considered formation epochs.