Time Travel can be a mechanism or a Template.
The sterling examples are the earliest uses of the mechanism, before the template was thought of. The British Barbarians uses a tourist/researcher from the future as a way to demonstrate how barbaric the preening, self-congratulatory Late Victorian English could look to a culture really advanced — in short, to remind them they still had a long way to go before they could consider the problems of the world and society solved. The Time Machine is on the Long Sleeper Template to visit a dystopia. The only reason to have a machine with a reverse gear is so the Traveller could return to his own time and tell his story to a friend in the frame, before disappearing again, never to be seen. Otherwise, the character “wakes up” (stops the machine) in a future age, has adventures, and the story could end right there. Wells tacks on some pointless vignette visits of the dying Earth after humanity has vanished.
The Time Travel Template, on the other hand, is wrapped up with the nature of time, fate, destiny, luck, free will, and alternate history. The time-traveller must use time travel to try to solve plot problems, which requires that the travel be controllable to some tiny extent. It’s up to the author to decide what they want or need: the “many worlds” of quantum theory or a monolineal timeline, rigid fate or conservation of history, or the easy fracturing into time branches that lets you kill your grandfather and still exist because you came from some other time branch where he didn’t die.
A story where the character simply stumbles through a hole in time at convenient (to the plot) moments is not on the Time Travel Template, but only using time travel as a mechanism.
Mechanism or template, the means of time travel are, by most realistic extrapolations of physics, all fantasy. You can mutter about Einstein and quantum-foam holding open wormholes, but those exorcisms won’t change that it’s highly unlikely to ever happen. So you can make it work almost any way you like to limit your traveller’s jumping around. Possible useful snags:
- It has to recharge between uses, so when you land some place, you’re there for minutes, hours, or days.
- It has finite energy, so you have to stop every so many centuries even in a high-speed run, and recharge. Picking rest points is an art.
- You have to keep a log, because you can’t be in the same time twice. After a while, whole decades and eras are “used up” for you. If you try to go there, you wind up at the nearest “empty” point forward or back. Multiply this by the number of travellers in a group.
- You can be in the same time twice, but if you run into yourself, the universe implodes, so stay out of that town.
- It’s a big honking device like a small submarine so you have to find somewhere to leave it, and walk away from it to do your visiting. It has to have great burglar-proofing. You may have trouble getting back to it.
- It’s tiny so you can carry it on your person, but that means it can be stolen, especially if it looks like a ring or other jewelry.
- It’s embedded in your tour guide, who was just carried off by the bandits.
So you can always make the time travel part of the problem as well as part of the solution.