I recommend at least two hours for couple's and wedding party portraits because I know that you will never again pay so much time, energy and money on your appearance than your wedding day.
You want to look your best and I want to capture it. Surely you wouldn't plan such an important day with so much attention to details without allowing quality photography time.
Family portraits can be done during the getting ready time and it takes 1,5-2 hours. You can read more about my tips for creating the wedding timeline here.