1985

James Blish said in conversation that his Midsummer Century begins in the "here and now." See Old And New. In one sense it does because the opening chapter accurately describes British and American society at the time of writing. However, the dates do not quite match:

Blish's introductory "NOTE" is dated 1971;
the work is copyright James Blish, 1972;
it was first published in England in 1973;
my Arrow edition was published in 1975;
Martels says that he was born in 1955 (p. 13);
he is aged 30 on the opening page;
therefore, Martels is time-projected from 1985.

This makes the opening chapter near-future or "day after tomorrow" sf, like CS Lewis' That Hideous Strength, published in 1945 and set "after the War." That gives the fictional new Sockette State University time to construct their radically new radio telescope with its unintended and unprecedented reach that projects Martels' consciousness to 25,000 A.D. The rest is future history.