Well, here's the bad news- every heifer is different, and they all pretty much need treated as such. That being said, there are some general techniques I use from year to year to make sure we hit our marks when we need to.
3-6 months of age: Let them eat. Put out a high quality, textured creep with Purina Precon, and basically have them self-regulate. This is when Sure Champ is introduced.
We wean when the cattle look right for it, but usually around 5 months.
Once they're in the barn, we really assess what each calf needs. More times than not, what they need is more feed, and usually with a touch less corn, and some added oats or barley. We generally feed the heifer calves pretty hard through our sales (first one is in September, second one in November), and back them down a little after NAILE. We will try to coast them into Denver as much as possible, especially if they are at peak showing condition. We actually don't want them 100% at this point, but it does happen occasionally. The introduction of additional fill such as Winning Fill, Depth Charge, Xpand-o, cotton seed hulls, or others is usually introduced at this point, but not all cattle need a bunch of extra fill at this point.
After whichever major is their last of the winter, we crash them pretty hard. Mostly put them on a free choice hay diet with a little supplementation and almost 0 corn. Maybe just a taste for energy if it's bitter cold. This is when we change them over to a barley/oat based feed, and really ramp up the fill if we haven't already. We will also usually feed a product like Fresh and Feminine or Femulate to really help smooth these girls up; we don't want to fight chests, tailheads, or udders in July/August.
Assuming we start our crash after Denver (middle of January), we will start to really feed the heifers like show cattle again in mid to late March, depending on how they look. They should maintain most of their body with being on a lot of roughage, but they should look a bit "dull" at this point. We want that, it gives us a goal to feed towards. This is when additional products such as Calf Mana, Show Bloom, and any "hair" supplements are starting to be fed if we're trying for a Jr National specifically..we might wait a couple weeks or up to a month to start on a state fair only animal.
Starting in the middle of April, your girls should start to look like show animals again, at least body condition-wise. I'm a big fan of feeding into a show rather than coasting if I can help it, so I may plateau the amount of feed the cattle are getting right about now. I want them to still be gaining some, especially the younger ones, but May is the real month for transformation. If you're feeding very much corn at all by April, there's a good chance you may lose the chest and udder in your heifers unless they're very hard doing. I will pull about 70% of our heifers off of a Fresh and Feminine type product about now, especially if they responded sharply to it. You can get one too hard with those products, but they are very useful in certain applications.
30-45 days before your target show, your cattle should be pretty ramped up on feed, unless you didn't get them tore down enough during your crash...this is when it gets tricky because this and the crash are the two places with a lot of divergence from animal to animal. Adjustments may need to be made every week or so during this period, with some cattle needing more bloom, some needing fill, some needing general weight, and some needing nothing but still need to be working towards looking 100% the day of the show. This is when Fresh and Feminine may be re-introduced with full feed to try to achieve the maximum amount of bloom but with minimum chunky fat blobs.
From there, you just kind of play it by ear. If one starts to tail off, reassess her, and adjust her feed accordingly. Maybe she didn't do well with barley as her main energy source these last couple of weeks, so she needs some liquid energy or a dollop of corn. Maybe one calf doesn't do as well with winning fill and needs more depth charge or cottonseed hulls. Maybe one heifer needs put on a round bale and fitter35 for 10 days before giving her any more real feed.
If anyone tries to tell you to just dump feed to a heifer the same every day for more than 60 days in a row, they either know some sort of dark sorcery that I'm not aware of, or they don't know what they're talking about.
TL;DR- Pay attention to the cattle. It's not rocket science, but you do need to take a close look at the girls at least once a week and adjust from there.