...mainly including Poul Anderson, of course.
The anonymous "Missing One's Coach" presents a visit to a historical period that might be a dream.
Twain's Connecticut Yankee experiences instantaneous "transposion of
epochs" to Arthurian Britain and returns to the nineteenth century by
Merlinian suspended animation.
In The Time Machine by
HG Wells, the Time Traveler and his dinner guests discuss "time
travelling" before the Time Traveler demonstrates his model Time Machine
which does not move anywhere but, remaining stationary on the Earth's
surface, undergoes extreme time dilation in either temporal direction
while also unaccountably becoming both invisible and intangible.
"The Dark Tower" by CS Lewis, five men discuss "time travelling" and
agree that it is impossible before one of their number demonstrates his
chronoscope which displays scenes not, as they initially think, from the
past or future but from an alternative timeline.
the Time Patrol series by Poul Anderson, timecycles, resembling
modenized Time Machines, instantaneously change their spatiotemporal
coordinates, thus neither moving nor dilating but disappearing and
In The Corridors Of Time by Poul
Anderson, "time travelers" really do travel through time because they
walk or drive down corridors whose lengths extend along the temporal
In The Dancer From Atlantis by Anderson, a
space-time vehicle does not remain stationary on the Earth's surface
but moves across it "...while traveling through time." (London, 1977, p.
In There Will Be Time by Anderson, some
mutants can "time travel"/dilate invisibly and intangibly without
needing a time machine and one of their number gives Wells the time
In The Time Traveler's Wife by Audrey Niffeneger, mutant time travel is instantaneous but involuntary.
In Bid Time Return by Richard Matheson and two Time novels by Jack Finney, travel to the past and back to the present is a learned skill.
"The Flight of the Horse" by Larry Niven, time travel is scientifically
impossible so it takes explorers into a fantasy past where they find
not extinct species but mythical beasts.
This is not
and cannot be a complete list of time travel fictions but it does cover
most of the possibilities and presents a conceptual sequence:
time travel is possible with machines - but there are different kinds of machines;
time travel is possible without machines - but in different circumstances;
time travel is impossible but time viewing is possible with a machine;
time travel is impossible so it is fantasy, not sf.