While on holiday, I borrowed, but did not finish reading, Stepsons Of Terra by Robert Silverberg.
(i) The characters refer to the "Absolute Past." Every moment is past to some moments but present to itself and future to others so there is no Absolute Past. The relativity of simultaneity means that event A can be simultaneous with event B to one observer but before or after B to another.
(ii) We are told that a building is safely invisible and undetectable because it is three microseconds in the past. It does not make sense to say that anything is now in the past. Even if it were somehow valid to say at 1.00 pm, "The building is now at 1.00 pm minus three microseconds," then, at 1.00 pm plus three microseconds, it would be necessary to say, "The building is now at 1.00 pm," so the building should be detectable at 1.00 pm.
(iii) Ewing is being tortured and is going to be killed but is rescued by an armed, masked man who returns him to his hotel room where he sleeps and recovers. On waking, he meets a group who have time travel. With their help, he travels a few days into the past to become his own armed, masked rescuer. After leaving his younger self asleep in the hotel room, Ewing continues to exist so he should still be in existence when his younger self has traveled into the past. This entails, on the simplest hypothesis, that there is a single timeline containing a single Ewing whose single world-line has a single loop.
However, Ewing concocts a much more elaborate scenario. He thinks that the Ewing whom he rescued is not only younger but also other and that this other Ewing will rescue yet another Ewing. The implications, not spelled out at least in the part of the novel that I read, are:
there is a succession of timelines;
pastward time travel is to the past not of the current timeline but of a succeeding timeline;
each Ewing is born, grows up and is eventually tortured in one timeline but is rescued by the Ewing from the preceding timeline and rescues the Ewing of the succeeding timeline.
Ewing feels obliged to end this regression. To do this, he leaves a written message beside his sleeping self advising that self not to travel into the past, then kills himself! This will ensure that the current timeline will continue to be inhabited by the Ewing who was born in it. It also ensures that, if there is a succeeding timeline, then it will be one in which Ewing is tortured and killed. Why the Ewing who kills himself regards this as a desirable outcome is beyond me.
Before dying, the Ewing who commits suicide reflects that the single factor for which he has made no provision is his own rescuer. That rescuer should have lived out the rest of his life in the preceding timeline. Either there has been an infinity of previous timelines or there has not. If not, then the Ewing of the first timeline could not have been rescued by a Ewing from any previous timeline so the progression could not have got started.
