Well, for speedrun purposes, around 29 seconds are automatically saved at the start of the run due to the opening being presented as an FMV rather than a slideshow of images that you have to skip individually.
Much like 505 GameStreet's other English localizations of Simple series games, Demolition Girl felt like the cheapest possible way to bring a budget game over to an English-speaking audience.
For reasons that we may never know, other changes included most of the Japanese voice acting being cut and replaced with text telling the player what to do, the ending FMV being presented as a slideshow as well, and the alien in "Farewell Giant Girl" appearing way smaller than it is in the Japanese version, though its hitbox remains the same.
Aside from these differences, both versions are nearly identical to each other.