Yes some versions are longer.
Actually here the creator of the game explains the differences between the various versions -
The PC version is also longer -
The PC DOS version :
The articles released at the time criticized the short lifespan of the Amiga version. So Delphine Software suggested I extend it. I had a few ideas left which were enough to make an entire level. However, I didn't want to break the global rhythm of the game, so it was impossible to add anything after the end of the game. The ideal location was just before the arena when the friend rescues Lester at the end of a long dead-end corridor. I decided to reinforce the close relationship between the hero and the alien, by developing their mutual aid. The only problem is that I only had two months to achieve everything. I was back on working 16 hours a day, 7/7. Eventually, that level brought a lot to the game. This version was ported by Daniel Morais.