I was out with my mate in Southampton, UK. When a set of girls pulled out a camera to take photos of each other. Obviously this situation requires another person from outside the group to take a group photo.
So there is your window of opportunity. My wing mans is unfortunately a bit of a wimp and I would have killed him had he not of approached the girls. Lucky he did after I prompted him and he ended up closing with a number.

So next time your out offer to take group shots!