The legion of time.

Denny Lanning and his Harvard roommates end up meeting again later in life, rescued at the moments of their death and traveling through time with eight other warriors recruited the same way. Their goal is a battle to decide the cosmic probability in favor of Jonbar, a utopia with (of course) a beautiful woman who visits Denny at points in his life and warns him. The villain is an evil woman (still beautiful) who wants to be immortal in the other probability option. She commands an army of insectoid warriors.

This book was first published as a serial in 1938, and this was the first science fiction concept of a crucial decision point in time travel novels - lookup the Jonbar Hinge on wikipedia. It is well done here, especially since the utopian outcome derives from a scientific mind that is starved of science in the other choice. The scenes of rescued warriors are also well done, even though each is mostly a caricature of their times - incidentally, this concept led to a time traveling role playing game called Timemaster.

After the legion is gathered, they gather information and fight skirmishes against the insects and their evil queen. Once they find out what they need (and where it is located), they stage an all out assault on the queen's palace, dying off one by one in a quest to reach the sacred object. These battle scenes are less well written and harder to follow. The final confrontation also feels a bit rushed. I'm wondering if the author jammed it all into one last episode for other reasons.

Gender bias as one would expect from a story written in 1938; characters are mostly flat though Denny and roommate physicist Wil McLan both grow some. A fairly quick read. Perhaps the story was reworked before being published standalone in 1952; it needed a bit more.