It's an odd thing, you may think the head instructor of a club trains around the clock, constantly honing their skills and keeping their edge. Even if you know that's not the case, it doesn't really hit you until you're in that situation. More specifically, it doesn't really hit you until you've been in that situation awhile and find yourself "suddenly" 20 pounds out of shape, and huffin/puffin after 10 minutes of drill.
So you've got 15 minutes before class, you've found a nice corner to hide in, so what do you do in such a small block of time that you won't injure yourself?
After doing a quick shake to loosen up all my joints, about 100 jumping jacks and maybe a nice slow naihanchi to warm up my legs, i'll throw a few stretch kicks, and find something to focus on.
An excellent drill to work on is what I call one-step shadowboxing. i'll find a corner or a mirror, and use my reflection to practice one steps. I don't practice them in the "traditional" way of starting from choonbee, kihap, etc, since that would like a little odd. I'm not working on perfect stances or targeting. Instead, I'm going for speed from hukuljaseh. One after another, one through thirty, and then back down to number one.
From there, I try to go right into my kick onesteps, doing the same thing. In this case, I'm really looking to try and flow from one kick to another, so sometimes, I'll do the one-step mirror image, so I can merge from one to another easier. I'm trying to do these as fast as possible, so by number 15, I'm usually a little tired.
Shadowboxing with one-steps is excellent for several reasons. First, it's a good aerobic workout, second, it allows you to visualize using your one-steps in a sprarring situation. I'll talk more about why you should be doing that later. Lastly, it's a great way to build your recall of all 90 one-steps.
More often than not, you don't get a chance to practice as much as you'd like anymore. When a student asks "what's number 27 hand technique?" you as the instructor must be able to recall it within a second. The longer it takes you to come up with it, the student loses faith in your ability and begins to wonder why there is such emphasis on memorization. After all, if the black belts obviously haven't memorized them, why should they?