As an instructor, being versatile is key, and one way to develop and improve versatility is to teach classes of different lengths. It is not much use only being able to teach classes of one specific length, but this is a problem I see very often. If you give a less experienced instructor a longer class time than they are used to, they will often rush through their material far too quickly, and run out of things to teach in the end of their class. Another interesting problem is that of short classes: can an instructor still deliver a worth-while class in 30 minutes?
I think that being able to deliver a 30 minute class that students still feel gave them good value for money is an excellent test of an instructor’s versatility. Giving classes of this length will require an instructor to be efficient, to not take up more time than necessary, and to pack as much value into every second as possible. All these skills will transfer over into longer classes as well, so the skills needed to teach a half an hour class will also be useful when teaching a three hour class.
With a short class, you can’t afford to waste time, so you need to look critically at every other element of the class, and ruthlessly cut out anything that isn’t necessary in order to run your class more efficiently.
For example, is your warm-up taking 10 or 15 minutes? If this is the case, then you’ve already lost a third or half of the class. The primary purpose of a warm-up is to warm-up the student’s muscles to help prevent injury, so if your warm-up includes lots of stretching for example, is this actually necessary, or does it simply take up time? In a longer class, you may want to include more stretching as you can afford to spend more time (although you should still be careful not to spend time unnecessarily), but this is not true in a shorter class.