The initiation of the project that led to the discovery of osimertinib at AstraZeneca was triggered in May 2009 at the Alderley Park research site, after forty compounds were tested in biochemical assays against the EGFR T790M mutant and wild-type forms of EGFR.
I believe this drug was first submitted in June of 2015 so roughly took 5-6 months to garner FDA approval: