It's a compilation of three novels about time travel. One of the stories in it (I forget which one) was mentioned and recommended by someone here on DU (I forget who) in a thread where we were discussing time travel paradoxes, particularly relating to historic events getting crowded with time traveling tourists from the future.
I ordered it via inter-library loan, and just picked it up last week. I haven't gotten through the introduction yet, but already I can tell that I am going to enjoy it based on the background and writing style of the author. I hadn't heard of Robert Silverberg before this, and I usually read non-fiction these days, but I am a fan of time travel stories, so I am looking forward to it.

In Times Three, Science Fiction Grand Master Robert Silverberg presents a trio of ingenious variations on one of science fiction's most durable time travel. These three novels, all of them prime Silverberg, approach that subject from a dizzying variety of perspectives. The result is a remarkable display of ingenuity, erudition, and sheer narrative power.
In Hawksbill Station, political prisoners from the 21st century are sent on a one-way journey to the late Cambrian era a half billion years in the past. Their struggle to survive the privations of this bleak, almost lifeless world forms the centerpiece of a deeply affecting account of loss, exile, and repression.
Up the Line, by contrast, is a comic/erotic romp featuring Judson Daniel Elliott III, Time Courier and tour guide to the wonders of the past. While on a routine assignment in ancient Byzantium, Jud unexpectedly encounters his true Heart's Desire, and his well-ordered life slides inexorably into chaos.
In Project Pendulum, identical twins Eric and Sean Gabrielson become the primary participants in the very first experiment in time travel. From a fixed point in time, they move by equidistant, steadily increasing arcs toward both the remote past and the unimaginable future. Their alternating viewpoints constitute a dazzling portrait of the wonders and terrors of a constantly evolving universe.
https://www.goodreads.com/book/show/10490124-times-three