parshanut torah comment - Purim fighting in Adar - why wait for 8 months?

According to the Purim timeline:

1. 
   

   the 13th of Adar (of the next year) was set as the target day for wiping the Jews.

   
   


2. 
   

   Mordechai became the vice in Nissan and the new decrees to fight Amolekites ware ruled and distributed on Sivan 23 of the current year.

   
   

Mordechai could command to exterminate all the supporters of Haman (or Amalekites or enemies in general) effective immediately, and not waiting for 8 months to see how the events would unfold.

He was still under the obligation of "הקם להרגך השכם להרגו" - to make a preventive fight.

Such an order would not contradict the first decrees that proposed that day for the extermination of the Jews. After all, whoever survives might fight the Jews on that day.

Why the commands to fights the Amalekites was postponed for Adar instead of immediately?