SNe II rate as a function of time for a constant star formation history over a period of 5 Myr. In the instantaneous star-burst case, the SNeII rate may be 10× higher at ages <10 Myr. We show the case of the vDC, SAL, CAN, and MKDP IMFs. Since only the MKDP IMF does not scale linearly with initial stellar mass, M_UCD, we show also the lines for M_UCD = 10⁷ M_⊙ and 10⁸ M_⊙; for the other IMFs we chose to plot only 10⁹ M_⊙. The arrow indicates that the peak of the SN II rate shifts to the left and upwards for a star formation history which is shorter than 5 Myr.