I have spent enough time around new Jiu Jitsu students to learn that they are not overly fond of warming up. Everybody loves learning new techniques and then trying those skills in live spars with an opponent. But there is a reason we do warm-ups before class everyday.
Brazilian Jiu-Jitsu is a contact sport. Injuries do happen. The thing we do to help minimize the risk of injuries is warming up. Stretching and running and doing squats may seem like they are just designed to make you tired. However it is all designed to limber up your body and get your muscles prepared for the training ahead.
So if you think that missing the first 20 minutes of class each day is ok, you may soon find yourself with a muscle strain that you could have avoided if you had been in class!