The choice of the time and duration of the prayer arises from a determined will, revealing the secrets of the heart. One does not undertake contemplative prayer only when one has the time: one makes time for the Lord, with the firm determination not to give up, no matter what trials and dryness one may encounter. One cannot always meditate, but one can always enter into inner prayer, independently of the conditions of health, work, or emotional state. The heart is the place of this quest and encounter, in poverty ant in faith.
Source: Catechism of the Catholic Church (Vatican.va)