Quote: "A PAL to NTSC conversion affects the running time of the final product by about 4%."

Not exactly. It's not the Pal to NTSC (and neither the NTSC to Pal) that affects the running time of the final product.

More exactly a master in Pal (25fps) is shorter than the movie's running time in theaters (24fps). But if you use THIS Pal master to make NTSC conversion, the shorter running time remains the same. If you want a "correct" running time, you must make another master, in NTSC, from the film's print.

The same goes in the reverse of course. Some French videos (VHS and sometimes DVD) were made (in Secam or Pal) from an US NTSC master. In this case, the running time was the same than in movie theaters and not at all "affected". I verified this many times.