We have delayed the spoilers as long as we might. In the end, Kenneth and Darius board the time machine, it is surrounded by a bubble, and in a flash it vanishes before the eyes of Jeff, Arnau, and two government agents. We do not know where our intrepid duo goes or what they do, whether indeed they are the reason Belinda is alive, whether they save Darius' mother.
Yet in the denoument behind the voice-overs of closing thoughts, we see Kenneth and Darius racing through the woods. Maybe it is a flashback to their training. Maybe it is a look at where they are going. If it is the latter, it suggests that they have great adventures bouncing around through time.
That means trouble.
Certainly it is possible to visit the past and change nothing of significance. However, thanks to the butterfly effect--the concept that small changes can have large consequences--the more times and places they visit, the more likely it is that they will change something that matters. This is the more significant, given that Kenneth lives in what was his parents' home not far from the launch site, and the machine appears to remain stationary relative to the planet. There is a good chance he will encounter if not himself his parents or ancestors. We cannot guess what impact that might have. He might severely alter his own life, even undo himself.
Or perhaps not. A disaster might occur, but they might avoid it.