The idea is for a time travel drama. A scientist discovers that rifts in time, occur naturally. He uses time travel to solve the abduction of his sister, who was taken away, when he was a small boy. Another idea is for him to be on the run, from a shadowy organisation, who are from the future and want to eliminate his knowledge, in order that they can control time travel.
A story concept means nothing. I can tell you now, it has been done before. What matters is how you write it, the characterization, the flow, the imagery, all of it. There's no point to asking what other people think of the concept! They'll either say,"Sounds great," or, "it sounds like a ripoff of..." If the idea stirs you, write it. Then ask people what they think of the final story. After they tell you what they don't like about it, revise it, usually several times, until you're happy with it or until you throw up your hands and say the hell with it. Please read this thread about What is Plot Creation and Development? (and yes, this is a template post, which should give you an idea of how often this comes up. But you already know that, from your first post here over a year ago.)
I Like both ideas. the first one gives the man a reason to time travel but the second one seems more Sci-Fi
and it's way overdone on tv, plus you've no hope of getting a proposal for a new series looked at, unless you already work in the industry, or have a good track record as a screenwriter and an agent with good connections in tvland... of course it's been done to death in feature films, too, but there at least you have a chance to get it considered, if you can come up with some twist that hasn't been done yet, or can turn out a rehash of the trite and true [pun intended] so brilliantly, that it's new again... so far, you seem to have ripped off mulder's never-ending search for his sister and too many tv series and movies to list...
Like Cogito said. Its how you write it. all concepts have been done or thought of at one point. but doesn't mean the way you write has. If he figures out what happens to his sister does he save her? if so that will change what happens in the future. Time travel is a sticky thing And combine the two idea He wants to save his sister and learns and figures out time travel but this group from the future wants to stop him. So it doesn't mess up the future. see now you don't have to worried about picking one.
paradox The paradox is that he can't save his sister, aware of the consequences, however, he can find out who did it, and bring them to book. There will be plenty of twists, and chronicle the hurt he felt, and the pain going over old ground.
Marina, that's one huge turtle neck. OP, I prefer the second idea. I thin it gives you more to work with. But maybe you could mix both ideas up? He's on the run from a shadow government that want his knowledge or to erase it. But is it really because they want to control time travel? His sister that was abducted when he was little has something to do with this. Ah, holy crap, she is now the leader of this shadow organization from the future. When she realizes the grown man is her brother can she . . .
I think that this is the point of the story, that time is fixed and destiny predetermined. To the OP, you could read up on the theories of predetermined timelines and so forth and use these as inspiration. But bear in mind, however, that your story will not be sold on this concept, you need to bring a fresh angle to the whole time-travel schtick in order to get interest. Time travel is perhaps due a (small) renaissance on TV, but you will need to bring something unexpected to the story.
Twist The twist with me, is that there is more then one method of time travel. Time travel seems to have one fixed point, whereas there might be more then one way to travel in time. If time travel was commercially exploited, it would be very lucrative.