Speaking frankly I try and stay away from the lilt of phrases like “inner peace”. I don’t discuss it in that way (perhaps semantics) nor do I focus on such a thing in my own practice or in my teaching of others.
I think its definition is far too broad (and therefore each person hears something completely different when the word is used) and it has become a buzz word used for marketing.
In fact it is far more likely that an efficacious yoga practice will stir up latent, unprocessed emotions. They could be emotions of joy but could equally be emotions of sadness, fear, or anger.
Serenity, calm, bliss, a quieter mind…these things come in layers. And as practitioners of yoga I assure you the Universe is listening. Just when you start to say how peaceful you are the Universe will likely send a test your way. For this reason I merely advocate the experience of the practice whatever it may be. Some are calmed. Others energized. Neither is enlightenment.
Pragmatically speaking, it is quite possible to feel effects from three months of asana practice, depending of course on the teacher, the practice, the frequency, the commitment, the desire to grow, the diet, sleep, et al. It is, as always, a compound formula.