I was looking over the Wikipedia list of time travel stories and realized one I had read in the early 1980s was not listed.
It was a short novel, perhaps 100 to 150 pages in paperback. I recall it being a well-known author of the 1970s, on par with (for instance) Pohl (but not him, I checked). The cover I recall clearly, it showed a teardrop-shaped spacecraft with an eye-like porthole floating just above a desert-like ground, and the atmosphere (and thus most of the background) was a sick yellow color like the air was poisoned.
The plot involves the protagonist coming across a time-travel system being experimented with by a group of scientists. Using the device, they discover an alien spacecraft that had been abandoned there millennia ago. I believe they go into the past to retrieve it, as opposed to digging it up in the present. Adventures follow, including traveling to another planet where the equally-dead race's automated spaceport attacks them by heat and they escape just in time. Then they fly home, return to the present, the end.
If that sounds a bit dumb, even at that age I wasn't terribly impressed with the story. But I do seem to recall it being someone well known... hmmm, well-known author but dumb plot... now I'm thinking Piers Anthony. Nope, not him either.