The precursor time, T, is the time interval between the occurrence time of a precursor and that of a forthcoming earthquake with local magnitude, M_L. 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 M_L are compiled from scientific literature. The plots of T versus M_L 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 M_L for the b-value anomalies, foreshocks, Rn changes, and γ-ray emissions. The relationship of log(T) versus M_L 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 M_L. 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 M_L or some precursors suggest the possibility of earthquake prediction in future.