What's the use of imitators of plants versus zombies? Is it permanent? Is there a time limit?

Forever, like you brought sunflowers and imitators. So, in the battle, you planted a sunflower and needed to cool it for a while. Planting a sunflower, imitator sunflower has no cooling time, as long as there is enough sunshine, it can be planted. In other words, the cooling time of sunflower and imitator sunflower is calculated separately. In this way, there is basically no need to worry about not planting plants in the sun.