If your marinade has any type of acid - like balsamic vinegar or fresh lemon juice - it will act as a tenderizer and begin to break down the chicken giving you a more tender, juicy end result. That's why 30 minutes is all it takes for this Greek chicken marinade. If you marinate your chicken for longer than 2 hours, the acid will break down the chicken a bit too much and give it a rubbery texture.