Any time, at all times, once, many times, unceasingly, aloud or silently
Lord Jesus Christ, Son of God, have mercy on me, a sinner. ♫
or
Lord Jesus Christ, Son of God, while breathing in deeply
have mercy on me, a sinner. while breathing out slowly
or
Lord Jesus Christ, Son of God, have mercy on me.
or
Lord Jesus Christ, have mercy on me, a sinner.
or
Lord Jesus Christ, have mercy on me.
or
Lord Jesus Christ, while breathing in deeply
have mercy on me. while breathing out slowly
In The Way of a Pilgrim, the pilgrim advises, "as you draw your breath in, say, or imagine yourself saying, 'Lord Jesus Christ,' and as you breathe again, 'have mercy on me.'"