Methods and apparatus for increasing the accuracy of timing characterization of a circuit including at least one cell in a cell library are provided. One method includes the steps of: performing cell library timing characterization for the cell for prescribed first and second temperatures, the first and second temperatures corresponding to minimum and maximum temperatures of operation of the circuit, respectively; selecting one or more additional temperatures between the first and second temperatures; performing cell timing characterization for each process, voltage and temperature (PVT) corner at the one or more additional temperatures, as well as at the first and second temperatures; and performing timing sign-off for each PVT corner using the one or more additional temperatures, the timing sign-off being based at least in part on the timing characterization for each PVT corner.