one way speed of light? do you mean original, pristine photons / waves emitted emitted from an energy source are in instantaneous travel at infinite velocity? as compared to old, second hand reflected light? test, without any clocks:
easy: have an original light source beaming away, and reflected light beside it, and visually compare the start and arrival side by side instant at the start and finish lines. guarantee you that there is no difference between virgin and reflective light speeds.
Consider this, time is the first dimension, always existed, with uncreated energy. light in our young universe traveled since about 13 billion years. none of it is still circulating at infinite speed all has been stretched into radio wave length. we all send messages into the future, but everything we look at, or hear, is from the past. Max speed @ c.
instantaneous reaction at a distance is from entanglement, prior contact, not superluminal travel.