Ideally Lunging Strike should be at 21 FPA (APS between 1.968 and 2.043 according to breakpoints on Maxroll), so after procing Tec the third attack will be cast at 63 frames, or 3 frames after Tec is off cooldown.
It’s legendary so getting it without trading requires some luck (or grinding).
I didn’t get one until I was already on T4.