Predicted against real values for time steps in the test set. The median is plotted as a line, and the shaded region shows the range predicted by 95% of the models. The colours represent the number of time steps emulated. For example, the blue lines show the predicted evolution of the chemistry for 1 Myr compared to the actual value after 1 Myr. We note that the dust temperature error is stable as it is a function of UV and column density, which do not change.