The Great Silence is, to my mind, the most powerful and meaning monastic practice of them all. Normally this period during which all talking ceases begins after Compline (the last prayer office of the evening) and continues until after breakfast the next day. Remember, of course, that by breakfast time, the monks or nuns have already participated in early morning meditation and the office of Morning Prayer as well as the Mass. Monastic communities also have other times and places for which silence is the rule.
Here's something quite wonderful about the practice:
Silence is like a river of grace inviting us to leap unafraid into its beckoning depths. It is dark and mysterious in the waters of grace. Yet in the silent darkness we are given new eyes. In the heart of the divine we can see more clearly who we are. We are renewed and cleansed in this river of silence. There are those among you who fear the Great Silence. It is a foreign land to you. Sometimes it is good to leap into the unknown. Practice leaping.