Need a little bit of help on a custom spell

So I am currently making a TD, and I want one of my towers to have a Berserk ability that increases its attack speed for a certain duration. but then after that duration the tower has decreased attack speed for a while.

Right now I have made the berserk ability and I have made the "tired" ability (endurance aura with negative attack speed bonus), but I am unsure of how to do this. I would be able to do it if i used waits, but that would make it non multi instanceable.

Anyone know how to go about this? Thanks

Presumably, the ability cooldown time is longer than the combined durations of the bonus attack speed and the reduced attack speed. In such a case, your code need only support a single instance per unit and it should be doable with waits alone. When the spell is cast, wait for the bonus speed duration, then remove the bonus speed buff from the triggering unit and add the reduced speed ability, wait again for the reduced speed duration, then remove the ability from the triggering unit.