You're welcome! Please do trust your vet and give it as he suggested, just give the per quart amount. 5 days or 8 days, it doesn't matter, I'm sure he has a reason.
This is what people usually give
Treatment20% Powder9.6% LiquidFor 3-5 days1.5 teaspoons per gallon2 teaspoons per gallonthen for 7-14 days1/3 teaspoon per gallon1/2 teaspoon per gallon
Your vet may have a reason for using more, like maybe they think your rooster isn't going to drink enough...