The precursor time, T, is the time interval between the occurrence time of a precursor and that of a forthcoming earthquake with local magnitude, ML. The precursors are classified into four types of earthquake prediction with different time windows: long-term prediction (T = 3 to 10 years); intermediate-term prediction (T = 6 months to 3 years); short-term prediction (T = 8 days to 6 months); and imminent prediction (T ≤ 7 days). Since the 1999 Chi-Chi earthquake, the precursors for numerous earthquakes in Taiwan have been observed and studied. The values of T and ML are compiled from scientific literature. The plots of T versus ML are made for some precursors when the data sets are large with the values of T for respective events. Such precursors are the b-value anomalies, foreshocks, thermal infrared radiation anomalies, geochemical composition changes, radon changes, γ-ray emission anomalies, and total electron content (TEC) anomalies. There is a positive correlation between T versus ML for the b-value anomalies, foreshocks, Rn changes, and γ-ray emissions. The relationship of log(T) versus ML is also inferred for Rn changes. The precursor time for Rn changes is positively correlated with that for γ-ray emissions. The time difference between the precursor time for Rn changes and that for γ-ray emissions is positively correlated to ML. However, the plots for thermal infrared radiation, geochemical composition changes, and TEC anomalies are quite scattered and thus not any correlation can be obtained. The positive correlations between T and ML or some precursors suggest the possibility of earthquake prediction in future.