You'd be hard-pressed to find instances of a time machine earlier than the 19th century, just because the idea of a "machine" changed greatly during the industrial revolution. The emerging prevalence of scientific technology also contributed to the notion that "machines" could be used to reproduce phenomena previously thought of as magical or theoretical - like time travel. H.G. Wells is often credited with the first major representation of a potential technology that could send its operator to the past or the future in his 1895 novel "The Time Machine."

There are of course many speculative books before this period, however, that use the idea of time travel to elucidate other points. What I mean is that the device used for time travel is not the primary focus of the novel - a device may not even be present. The focus is more on anthropological, sociological, or political insights into the writer's own time.

Frederic Jameson ("Archaeologies of the Future: the Desire Called Utopia and other Science Fictions"), among others, have argued that early writings like Thomas More's "Utopia" (1516) are actually the beginning of the speculative literary tradition in its depiction of "primitive" cultures like the ones Europeans were encountering during pre-colonial explorations. The idea is that the European narrator is encountering a "past" culture that exists outside of any and all "civilized" European influence. Early writers like More used these isolated cultures to make anthropological reflections on how civilization progresses. Others, like Rousseau in the 18th century, ("Discourse on the Origin of Inequality") theorized what primitive humanity would look like, what natural laws it would foster, without the corrupting influence of governments (aka civilization). This naturally led writers to speculate on the FUTURE of civilization.

One of the earliest "speculative" books I know is Mercier's "L'an 2440" (The Year 2440), published in 1770. In it, a Frenchman from 1770 falls asleep and is not woken until the year 2440, in which he sees the positive conclusions that followed from French revolutionary politics of the 1770s. Basically, he sees a happy society that had overthrown their monarch and now live in a peaceful republic. As you can see, the emphasis is not on the future, per se, but on how to change the present to achieve that future.

It really only is in the late 19th century that writers integrate scientific achievement as we know it now into the already-present discourses on time travel. Other than the H.G. Wells, you might want to take a look at "A Connecticut Yankee in King Arthur's Court" (1889) by Mark Twain, or Jules Verne's "Paris in the 20th Century" (1864) - the latter which specifically critiques the 19th century's growing obsession with technology.

Kakudmi is a figure in Hindu Mythology that time travels as he's returned to earth after meting Brahma and finds many ages of man had passed.

Urashima Taro is a Japanese folktale about a fisherman who stays in an underwater palace and find out hundreds of years has passed on land while he was there. More 'time dialation' than time travel, maybe.