Prayer is an exercise of love and it would be incorrect to think that if there is no time for solitude, there is no prayer at all. For the very reason that prayer is based especially on love and springs from it, it is possible to prolong it beyond the time devoted exclusively to it.
Though it is not possible to be always thinking of God, partly because our mind gets tired, or because our many occupations demand full attention, still it is always possible for the heart to love and to desire God, and this can, and must, exist even in the performance of duties which absorb our intellect; in fact, such an orientation can be intensified by the desire to accomplish every action for the love of God, to please him, and give him glory.
"The reason for prayer" according to St. Thomas Aquinas, "is a desire moved by charity. . . And this desire with us must be continuous, either in act, or at least potentially. . . We can say that one prays continuously by reason of the continuity of his desire".
Fr. Gabriel of St. Mary Magdalen, OCD