How often should I practice yoga to experience the benefits ?

The more often you practice, the better you will feel. Even if you practice once a week, you will progress steadily. Once you feel confident enough you can start practicing at home between group classes (15 minutes a day is enough to start). You can adapt your practice to your schedule, your energy level, or whatever you feel physically or emotionally. It’s better to do a little bit frequently rather than too much irregularly.