No, not true. In 30 minutes, you are unlikely to have time to complete the entire planned exercise program and give a full load to the muscles.
If you are working to gain muscle mass, then the workout really should not be too long and exhausting. You need to do it in about 45-60 minutes. Nothing can be done in half an hour, tk. you will be training with heavy weights and need quite long breaks between sets (up to 3-5 minutes in some exercises). To this add 10 minutes of warm-up at the beginning. And at the end of the workout, it would be nice to do stretching, this is good for muscles and a beautiful relief.
If you are working to lose weight, you will hardly have time to do a circular workout in half an hour. In a hurry, it is easy to get injured, and the heart will be a serious burden. But even if you miraculously do this, then for weight loss you will also need to do cardio. And this is at least half an hour.
So in any case it will not be possible to spend less than 1-1.5 hours in the hall.
The optimal time for strength training for "non-athletes" is 40-60 minutes. Plus about 20-30 minutes of cardio training: jogging or brisk walking on a treadmill.
I heard that even professional cyclists devote no more than 1 hour 20 minutes to strength exercises per workout.
This is related limitation, first of all, with an increase in the blood hormone cortisol during training (if you are interested - about it here: sports-is.ru).
Cardio training is not a warm-up. It has a specific goal: to burn excess calories, and, accordingly, excess fat. The optimal heart rate is calculated from the formula 220 minus age (for men) and 216 minus age (for women). If you are just starting to exercise, divide the figure obtained by 1.5 (and do not increase at least 2 weeks).
The process of burning calories occurs only during cardio training. Once stopped, the process stops. At the same time, the effect of strength training continues for 36 to 72 hours. Therefore, when exercising 3 times a week, it is recommended to train different muscle groups on different days so that they have time to rest and recover.