I can tell you that no two pastures are alike, even if neighboring. The only way to know what your soil needs, and therefore your grass, is what Stocker Steve said....soil test, soil test, soil test! I was instructed by Dr Paul Mislevy (retired Univ of Florida Professor-Retired, and friend/client of mine), who has developed or co-developed a ton of the different strains of grasses used today, to apply fertilizer when the rye is about 4 inches in height....but ONLY after testing the soil. This was Florida, but I would suspect the same principles apply elsewhere.
Remember, there is no "cookie cutter" fertilizer plan. You need to have soil samples tested if you want the most bang for your buck.