The way to approach what the fields are, at a distance, is EM Wave theory (macroscopic). A particle (microscopic) in the field that you will then have calculated will "feel" the field as it is at a particular time. That's in the definition of a Field.
You would know about an event, 1 LY away, One Year 'later'. But the light / EM pulse you originally produced took One Year to get there, so you could say that you would know that you had caused something to happen 1LY away, 2Years later.
Circuit theory was really not designed around that sort of a problem. The nearest way to get an answer to that sort of question would be to approach it in terms of a transmission line, which is a macroscopic approach. That approach looks at the wave as it propagates and gets reflected at discontinuities. After sufficient time, the impedance, seen by the source at the transmitting end, will settle down to a steady value after all the significant internal reflections in the line have finally reached back to the source. In a 'sensible ' length of line, this could involve several transits of the line. Loss in a very long cable could mean that you would have no idea of just how far your signal got; it could have been dissipated on the way.
How practical or ideal did you want the model to be?