It depends. Half a millisecond is, I believe, around 7" worth.
However, interferometry teaches us that small misalignment between drivers and crossover implementations would be completely audible even at a few millimeters.
So, matching your tweeter to midrange to woofer electroacoustically is critical.
Despite many studies we have never seen consistent acceptance or demand for speakers with perfect phase/delay response.
What is my point to all of this? That delay mismatches are complicated.
However, interferometry teaches us that small misalignment between drivers and crossover implementations would be completely audible even at a few millimeters.
So, matching your tweeter to midrange to woofer electroacoustically is critical.
Despite many studies we have never seen consistent acceptance or demand for speakers with perfect phase/delay response.
What is my point to all of this? That delay mismatches are complicated.