Someone related this question at the s'udas Purim:
Haman's decree was promulgated on the 13th of Nisan and would not take effect until the 13th of Adar following. Yet, Mord'chay urged Ester to seek redress from Achashverosh immediately. This would not be surprising, except that she had told him she had not been called to Achashverosh in a month, so was risking her life: why not wait until she would be called (which would surely happen with time to spare before Adar)?