While in my teens and 20's each class has about 10 minutes of stretching - hams, back, shoulders and neck. (I was never good at splits as my legs just didn't go that way). At that age I could do roundhouse kicks to the head and sidekicks to the upper chest with good form and power. After that time, I only spent 1 or 2 minutes on it before workouts and then concentrating more on relaxing the muscles than stretching. I think they are two different things. That's it, even before sparring.
I never strained a muscle from lack of stretching. In fact, I've found stretching more dangerous. Since leaving competition I have little need for high kicks, preferring the Okinawan way of lower kicks for self-defense. Now as an old guy my tendons and muscles are losing some elasticity so 3 times/week at the gym I do 5 or 6 minutes of stretching to keep mobile (and to rest between sets of weights).
Although I've managed well spending minimum time on stretching, I am not recommending to others not to spend time on it. It's probably a good idea for most everyone. But learning how to relax and not over-reach your technique is IMO just as important to avoid injuries.
