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When taking baby Aspirin and having anticipated bleeding (e.g. planned surgery or dental work), hematologist's advice was to start preparing about two weeks in advance: take pill every other day for about a week, then stop for another week.

This paper tells The American College of Chest Physicians' recommendation is stopping 7-10 days in advance, in the clinical study they measured 96 hours (4 days) for "normalizetion of platelet reactivity":

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4008770/

But please speak with your own doctor(s), your medical situation may differ.