Well mayby thay did hold out longer, we see them, then the tent, then them asleep... we didn't see them finish..so to speak, and I am not sure the holding hands was anyone finishing, I think it was Jack holding on for dear life cause I have a feelling I shouldn't say what I was thinking here 
I thought the grunting from Ennis and the collapse from Jack meant they were finished! My god, I've long forgotten what it was like to be 19 
LOL !! Me too. Oh to be 19 again.
Maybe they were just finished for that round !?
I also thought that the grunting and Jack's collapse meant that they were finished, and it was way too fast - if not for them, then for me! But I don't think there were any more rounds, according to the story after the first one it was "out, down and asleep". I wonder why Larry and Diana didn't include "gun's going off" in the screenplay... Just imagine Jack/Jake saying that in the movie, WOW, that could be really
really sexy... I think if he said that I would've finished... (did I just say that??! :o no, I didn't say that... ignore that one, please!!)
OT, about the holding hands thing - for any of you who'd seen "Priest", there was a part there when they held hands while they were having sex and the camera focused on their hands, you could realy see how it was done out of passion, I thought it was very beautiful.