i think that if you do a global variable for this, all your enemies will attack you at the same time. better use private variable for your enemies:
start of layout: set enemy.timer to int(9-(random(6)))
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every enemy.timer seconds: kick player; set enemy.timer to int(9-(random(6)))
int(9-(random(6))) - i think, this expression gives better results than just int(random (3,9))