Place it at the exact frame of the cute reveal, after any intro sting has finished. Follow it with the romance sound effect for a couple reveal, or precede it with a bell ding sound effect to cue attention first.
About this sound
This is a three-second human vocalisation, a soft and drawn-out 'aww' delivered as a single reaction. It feels warm, charmed and lightly sympathetic, the sound people make for something sweet or a little sad, and that mix of affection and gentle letdown makes the emotion instantly clear.