Going back to Christopher Bennett, I'd say Watching The Clock is the most hard sci-fi a story about time travel could possibly be.
Well, let's say it's as hard-SF as I could make a novel about Star Trek
time travel. There are certainly more solid hard-SF time-travel novels out there, many of which I drew ideas from -- things like Timescape
by Gregory Benford, The Time Ships
by Steven Baxter, and Timemaster
by Robert L. Forward.