I can tell you that every calf is different, you can use past experiences in feeding, weight gain, and finish weight as a gauge, but will need to adjust as you go. A calf at your calf's weight needs to be getting 3 percent of his weight in feed daily, once they hit 1200 to 1250 you can slow their weight gain down and hit your/their target weight at the right time. I prefer to have them at their target weight a few weeks prior to the the show, go past their target weight and pull them back for weigh in. Some calves look perfect at 1250 to 1300 others need 25 to 100 pounds more to look their best, (they can cross the scale at or near 1300 but can enter the ring weighing 1325 to 1375)
Holding or slowing a calf down the last month or 2 is easier than trying to get 100 to 150 pounds on one in the heat of the summer. Beet pulp, soy pellets and stabilized rice bran and a few pounds of oats a day, can keep one looking good but gaining slowly. I will bet most of your grand champions at the majors hit or passed their target weight at least a month prior to the show (if not 2 or 3 months earlier)
Push him now, cruise later.
