1. Start with a coverage pass, not a target
Move slowly over the whole triangle — clitoral head on top, both sides of the opening below — at low intensity, pausing at each point long enough to see a response before moving on. This pass is how you find out where she wants you to come back to; it's not a better way to touch, and if her feedback points to one place, staying there is the right answer.
There's no stopwatch answer to how long per point. A clear positive response means staying longer is the point; no response, or an overload signal, means move along. Feedback is the clock — and it isn't static: the same spot can respond differently at low arousal than at high, so what worked ten minutes ago may need re-asking.