Intention or words?
The moment you intend to invite the angels and the moment you start saying:” I invite my angels to heal ...” you would feel some energy touching your body. This is a variable feeling - some people find it like tingling, other people find it like warmth. During the healing you might feel the angels working where you asked them to. Or, you might need a while to feel them. The more you practice, the more you would feel them.