Buck urine is a territory type scent and is usually used throughout Pre-Rut & during the rut. In theory this scent is meant to lure in mature bucks only but not always. Spray it in and around areas with signs that show another bucks territory but remember this could intimidate a younger buck and he may leave that area. In my opinion this scent is most effective during pre-rut.
During the full swing of the rut, estrus scents are more commonly used. Just because this is more of a wanted scent by a buck at this time of the season. This scent mimics a doe that is ready for mounting and usually thats the only thing on a bucks mind during the rut.
Personally I prefer to just use scent eliminators and cover scents. Ive had just as much success with these if not more in the woods than I do trying to pretend I'm another deer.