Alternatively, you could have a timer that is set to expire in 5 seconds if a hero kill another hero, but is reset to 5 seconds again another hero is killed, while adding +1 to an integer variable. When the timer ran out, you would check the value of the integer variable.
This way, however, is incredibly complex in GUI (Triggers), and would probably not be worth it in the long run.
P.S. -- «How to» threads go on the World Editor Help Zone.
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