The Time Machine uses time travel to present a dystopian future whereas the same author's The Shape Of Things To Come uses a fictitious historical text book to present a utopian future. Thus, these two works remain distinct and separate whereas:
Olaf Stapledon's fictitious history, Last And First Men, culminates in the Neptunian Last Men who mentally time travel to earlier periods;
Robert Heinlein's Future History culminates in Lazarus Long who (unfortunately) physically time travels to the early twentieth century;
Isaac Asimov's incoherent time travel novel, The End Of Eternity, (unfortunately) connects with his Robots and Empire future history.
Although Poul Anderson's future history series, the History of Technic Civiliation, and his time travel series, the Time Patrol, remain distinct and separate, the same author's time travel novel, There Will Be Time, connects with his Maurai future history. As ever, Anderson explores both possibilities.
Although Larry Niven's Known Space future history contains one story that implies time travel, Niven develops the latter concept in other works, including his Svetz series. As yet, SM Stirling has written alternative, not future, histories, and therefore has written about alternative timelines, not about time travel.