A method includes: receiving a library associated with a cell; determining a plurality of candidate hold times for the cell; acquiring a plurality of candidate setup times corresponding to the plurality of candidate hold times, wherein a data delay associated with each of the candidate setup time fulfills a data delay constraint for the cell; adding the plurality of candidate setup times to the plurality of candidate hold times, respectively, to obtain a plurality of candidate time windows; and selecting a target time window having a minimal time span among the candidate time windows. At least one of the receiving, determining, acquiring, adding and selecting steps is conducted by at least one processor.