Why do I only practice it for a minute or so each day?

Imagery is like a firework display. You need only a single match to ignite a cascade of fireworks: So for a micro input you get a macro response.

Like any medicine, you need to repeat it generally three times a day for 21 days. Twenty–one days is a natural cycle of the human body. Research has shown that it takes up to 21 days to break a habit.