The 3 second rule can also be the 30 second rule. Just as long as you approach with confidence and demonstrate to a woman survival, emotional and practical value when you do.
Quality of interaction is more important than the quantity of time that you allow to elapse from initial glance to approach. That rule was simply invented to battle your inner demons from talking you out of the approach.
For the most part and the important part is that you propel yourself to act and if this is a tool which allows you to do that, great. Mind you, in some instances logistics may have to be considered. For instance, a woman may be having a serious conversation about something serious and so if you approach her without calibrating this, that will make you look socially non-calibrated and retarded if you don't at least wait for a more proper opening.
So you need to find a convergence point between conditioning the gut level need to act with external circumstances and logistics so that you not only open but can carry on the interaction to a successful completion.
McMaax
http://www.maaximumseduction.com