"Bid Time Return"

Years ago, a British astronomer told me that any time gained from time dilation on an outward journey would be repaid on the return journey so that there would be no difference at the end of a round trip. However:

How does the universe know the difference between an outward and a return journey?

If the equations entail his conclusion, then why does anyone think otherwise?

This is where Poul Anderson fans would benefit from a scientific education. But there must be blog readers out there with informed opinions on this matter? The astronomer's view would not affect works, like Tau Zero or The Boat Of A Million Years, in which there is no return journey but would invalidate the Rustum and Kith Histories and "Time Lag" - although, on the other hand, all hard sf reflects the scientific understanding of the time when it was written.

Regular readers might have noticed that this blog averaged eight posts per day for the first five days of May. This rate of productivity cannot possibly be sustained. I happened to be rereading The Boat Of A Million Years which is long and full of condensed information so that post followed post very easily. We have now returned to a more sedate pace.

Time Lag

Poul Anderson, "Time Lag" IN The Collected Short Works Of Poul Anderson (Framingham, MA, 2009), pp. 241-265.

Traditionally, Rome was founded in 753 BC. Some Roman historians counted years AUC, Ab Urbe Condita, "From the Founding of the City." Poul Anderson's "Time Lag" is divided into five sections headed:

522 Anno Coloniae Conditae 
538 A.C.C.
553 A.C.C.
569 A.C.C.
584 A.C.C.

Thus, the narrative covers sixty two years of the human colony on the extra-solar planet Vaynamo which has thirty hour days and natural equivalents of elves.

The Alfavala:

live in nests;
are "...wild little folk...," flitting and twittering, with glowing eyes (p. 241);
have "...long ears, flat nostrils, feathery antennae...green hair..." (p. 242);
either keep to the forests or serve men like dogs;
can speak a few words and use simple tools;
are more animal than rational;
are safe to be with because sensitive to danger;
but not essential to the story -

- and, although I have read "Time Lag" at least twice, I had completely forgotten these Vaynamoan natives until I reread the opening passage in The Collected Short Works.