It definitely *can* be done on TV -- as mentioned above, _Continuum_ is great, and _Dark_ might prove to be. The key is (a) the series needs to take a really clear stand on how time travel *works*, and work hard to be consistent, (b) the way it works needs to be limited enough to not degenerate into deus-ex-machina chaos, and (c) you need to know where the story is going.

_Continuum_ always had a planned conclusion -- indeed, the point where I fell in love with it was somewhere in season 2, when I realized that there was only one possible ending that both fit everything we knew *and* would be satisfying from a story POV (and yes, that was more or less precisely the ending we got). I had guessed that they had intended seven seasons based on pacing, and I've heard plausible rumors that they originally intended ten; in practice, it got cut off at three-and-a-half, but with just enough warning to pull the story together in that final half-season. (Albeit with some plot lines that clearly got chopped off at the knees -- what I suspect was probably intended to be the entire plot of season five got crammed into five minutes of explication.)

_Dark_ -- don't know whether they actually have the story fully mapped, but it certainly *feels* like they do, in the way the threads keep tying together. Certainly they're mapping at least each season in gory detail, although I don't know how deep the overall story bible goes...