What is the "light" part in a light-year, a light-second, a light-micro-second, whatever? Is it particulate? Come to that, what has space really got to do with time? Space is a matter of "concurrent", thus space's time is also a matter of "concurrent". Contract the space -- in "space-time", contract the time -- in "space-time". Expand the time, expand the space. Four-dimensionality means FOUR-dimensionality, not ONE-dimensionality. So both space and time, at least local universe-wise are a matter of relativity; a matter of bubble universe plasticity.
Time does have physicality, 3-dimensions worth of physicality, positive (+), negative (-), and resulting third dimensional '0' (real space, real time, 0-point, aka most local "position" ("velocity" uncertain, if not unknowable, to the max) regarding the principle of uncertainty)). Positive (+) time = from the Big Bang / Planck horizon to 0-point. Negative (-) time = from 0-point to the Big Bang / Planck horizon. If the Universe is infinite, if it has any infinity at all to it, even one -- even the concept of it (then it is infinite all the way). Then the non-local, non-relative, Universe (U) is forever timeless (0).
Positive time (+) from the Big Bang / Planck collapsed horizon of infinity passes no 0-point center point of infinity by. Finitely, though, it mirrors; is a time mirror ("time's mirror") into negative time (-). Time negative (-) from 0-point to the Big Bang / Planck collapsed horizon is a little bit different, a future 'past' (versus past 'future'). From horizon to mirrored horizon mass energy and heat collectively accumulates to each and every point of that collapsed horizon in its multiverse dimensionality (a collapsed horizon that forms, results in, an infinity of infinitesimal / finite point-bubble universes wide and deep); until Planck / Big Bang mass energies, heat, and time, is reached (until the [Planck / Big Bang / 'c' / ?] in a distantly finite constant of collapsed horizon is reached). Time forward (+): Time reversal (-): Time '0' ((+)(-)). Three co-existent dimensions of space and time, super-position correlative dimensions.
If they were particle, they would probably be photon (space-time forward)-tachyon (space-time reversed) paired (or something like that). Maybe even the elusive 'graviton' (the baby blackhole(s)?). Who knows.