As a certified fitness instructor, I was always taught to use the bell curve model, which was mentioned by the preceding people who answered your question.
Dynamic warm ups can be about 5 minutes in length or longer depending on the type of class and the participants. For example, you would want the warm up to be longer and more dynamic & fluid in monition if you are teaching a class with senior citizens or less fit individuals. The dynamic warm up can be 5 minutes if you are teaching a class to mostly younger or more fit individuals.
The cardio portion can be anywhere between 30-40 minutes, again depending on your type of class. You will want to cool down for about 5 minutes or longer depending on your class. You can also offer a few minutes of strength training or balance training.
I always make sure to have at least 5-10 minutes of stretching because most people don’t do enough stretching and it is a good way to incorporate some relaxation.
Hope this information helps!