But there is no chronology involved. It could have been a week or a month or years. But there is no necessity in the text to take it back to her conception. That is purely a matter of theological presuppositions. In the RC worldview Mary MUST have been conceived without sin.
And that the "graced" state is complete and perfect.
If by "complete and perfect" you mean it was impossible for her to sin, then, no, it does not mean that. It was complete only in the sense that God, the author of her salvation, justifies His saints by the imputed righteousness of Christ, and briung us by the process of sanctification to a state of glory without regard to our estate.
Catholics don't believe it was impossible for Mary to have sinned, only that she didn't.