I was just wondering, is it immediately, few seconds or a couple of minutes??
Almost immediately.
From my experience, for best effect, spray the pheromones about 5 - 10 minutes before you meet your target. For oil-based phero, apply about 20 - 30 minutes before you meet your target.
In a small enclosed space–e.g., car–almost immediately with strongest impact in 5-10 minutes. In open spaces it varies considerably depending on distance, air flow and population density.