A Look!

I have read about the 3 second rule to prevent AA, but my question is this?

When just going about your normal business you see a nice looking woman working towards you or on the other side of the office, you notice she has looked your way or is just passing, how long do you hold that look? Same as above 3 seconds or till the woman looks away?

I might let on but not after anything else but to see what response I get from the look of acknowledgement. Does this make sense in what I’m asking?